rfc8826xml2.original.xml   rfc8826.xml 
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<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [ <!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
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<!ENTITY RFC7675 SYSTEM "http://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC
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<!ENTITY I-D.ietf-rtcweb-security-arch SYSTEM "http://xml2rfc.ietf.org/public/rf
c/bibxml3/reference.I-D.ietf-rtcweb-security-arch.xml">
<!ENTITY I-D.ietf-rtcweb-overview SYSTEM "http://xml2rfc.ietf.org/public/rfc/bib
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]> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" submissionType="IETF"
<?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?> category="std" consensus="true" number="8826"
<?rfc toc="yes" ?> docName="draft-ietf-rtcweb-security-12" ipr="pre5378Trust200902"
<?rfc symrefs="yes" ?> obsoletes="" updates="" xml:lang="en" tocInclude="true" tocDepth="4"
<?rfc strict="yes" ?> symRefs="true" sortRefs="true" version="3">
<?rfc compact="yes" ?> <!-- xml2rfc v2v3 conversion 2.34.0 -->
<?rfc sortrefs="yes" ?>
<?rfc colonspace="yes" ?>
<?rfc rfcedstyle="no" ?>
<!-- Don't change this. It breaks stuff -->
<?rfc tocdepth="4"?>
<rfc category="std" docName="draft-ietf-rtcweb-security-12"
ipr="pre5378Trust200902">
<front> <front>
<title abbrev="WebRTC Security">Security Considerations for WebRTC</title> <title abbrev="WebRTC Security">Security Considerations for WebRTC</title>
<seriesInfo name="RFC" value="8826"/>
<author fullname="Eric Rescorla" initials="E.K." surname="Rescorla"> <author fullname="Eric Rescorla" initials="E." surname="Rescorla">
<organization>RTFM, Inc.</organization> <organization>RTFM, Inc.</organization>
<address> <address>
<postal> <postal>
<street>2064 Edgewood Drive</street> <street>2064 Edgewood Drive</street>
<city>Palo Alto</city> <city>Palo Alto</city>
<region>CA</region> <region>CA</region>
<code>94303</code> <code>94303</code>
<country>United States of America</country>
<country>USA</country>
</postal> </postal>
<phone>+1 650 678 2350</phone> <phone>+1 650 678 2350</phone>
<email>ekr@rtfm.com</email> <email>ekr@rtfm.com</email>
</address> </address>
</author> </author>
<date month="July" year="2020"/>
<date year="2019" /> <!-- [rfced] Please insert any keywords (beyond those that appear in
the title) for use on https://www.rfc-editor.org/search. -->
<keyword>example</keyword>
<area>ART</area> <abstract>
<workgroup>RTC-Web</workgroup> <!-- [rfced] In this cluster, we have been expanding WebRTC in the body of the
document (but not the title) as Web Real-Time Communication. Do you want to
include this expansion somewhere, or is not needed with the current
explanatory text?
Original (first occurrence):
WebRTC is a protocol suite for use with real-time applications that
can be deployed in browsers - "real time communication on the Web".
This document defines the WebRTC threat model and analyzes the
security threats of WebRTC in that model.
-->
<abstract>
<t> <t>
WebRTC is a protocol suite for use with real-time applications that can WebRTC is a protocol suite for use with
be deployed in browsers - "real time communication on the Web". This real-time applications that can be deployed in browsers -- "real-time
document defines the WebRTC threat model and analyzes the security threa communication on the Web". This document defines the WebRTC threat
ts of model and analyzes the security threats of WebRTC in that model.
WebRTC in that model.
</t> </t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section title="Introduction" anchor="sec.introduction"> <section anchor="sec.introduction" numbered="true" toc="default">
<name>Introduction</name>
<t> <t>
The Real-Time Communications on the Web (RTCWEB) working group has stand ardized The Real-Time Communications on the Web (RTCWEB) Working Group has stand ardized
protocols for real-time communications between Web browsers, generally protocols for real-time communications between Web browsers, generally
called "WebRTC" <xref target="I-D.ietf-rtcweb-overview"/>. The called "WebRTC" <xref target="RFC8825" format="default"/>. The
major use cases for WebRTC technology are real-time audio and/or video c alls, major use cases for WebRTC technology are real-time audio and/or video c alls,
Web conferencing, and direct data transfer. Unlike most conventional rea Web conferencing, and direct data transfer. Unlike most conventional rea
l-time systems, l-time systems
(e.g., SIP-based <xref target="RFC3261" /> soft phones) WebRTC communica (e.g., SIP-based <xref target="RFC3261" format="default"/> soft
tions are directly controlled phones), WebRTC communications are directly controlled by some Web
by some Web server. A simple case is shown below. server. A simple case is shown below.
</t> </t>
<figure anchor="fig.simple">
<figure title="A simple WebRTC system" anchor="fig.simple"> <name>A Simple WebRTC System</name>
<artwork><![CDATA[ <artwork name="" type="" align="left" alt=""><![CDATA[
+----------------+ +----------------+
| | | |
| Web Server | | Web Server |
| | | |
+----------------+ +----------------+
^ ^ ^ ^
/ \ / \
HTTP / \ HTTP HTTP / \ HTTP
or / \ or or / \ or
WebSockets / \ WebSockets WebSockets / \ WebSockets
v v v v
JS API JS API JS API JS API
+-----------+ +-----------+ +-----------+ +-----------+
| | Media | | | | Media | |
| Browser |<---------->| Browser | | Browser |<---------->| Browser |
| | | | | | | |
+-----------+ +-----------+ +-----------+ +-----------+
Alice Bob Alice Bob ]]></artwork>
]]></artwork>
</figure> </figure>
<t> <t>
In the system shown in <xref target="fig.simple"/>, Alice and Bob both h In the system shown in <xref target="fig.simple" format="default"/>, Ali
ave ce and Bob both have
WebRTC-enabled browsers and they visit some Web server which operates a WebRTC-enabled browsers and they visit some Web server that operates a
calling service. Each of their browsers exposes standardized JavaScript calling service. Each of their browsers exposes standardized JavaScript
calling APIs (implemented as browser built-ins) (JS) calling APIs (implemented as browser built-ins)
which are used by the Web server to set up a call between Alice and Bob. which are used by the Web server to set up a call between Alice and Bob.
The Web server also serves as the signaling channel to transport The Web server also serves as the signaling channel to transport
control messages between the browsers. control messages between the browsers.
While this system is topologically similar to a conventional SIP-based While this system is topologically similar to a conventional SIP-based
system (with the Web server acting as the signaling service and browsers system (with the Web server acting as the signaling service and browsers
acting as softphones), control has moved to the central Web server; acting as softphones), control has moved to the central Web server;
the browser simply provides API points that are used by the calling serv ice. the browser simply provides API points that are used by the calling serv ice.
As with any Web application, the Web server can move logic between As with any Web application, the Web server can move logic between
the server and JavaScript in the browser, but regardless of where the the server and JavaScript in the browser, but regardless of where the
code is executing, it is ultimately under control of the server. code is executing, it is ultimately under control of the server.
</t> </t>
<t> <t>
It should be immediately apparent that this type of system poses new It should be immediately apparent that this type of system poses new
security challenges beyond those of a conventional VoIP system. In parti cular, security challenges beyond those of a conventional Voice over IP (VoIP) system. In particular,
it needs to contend with malicious calling services. it needs to contend with malicious calling services.
For example, if the calling service For example, if the calling service
can cause the browser to make a call at any time to any callee of its can cause the browser to make a call at any time to any callee of its
choice, then this facility can be used to bug a user's computer without choice, then this facility can be used to bug a user's computer without
their knowledge, simply by placing a call to some recording service. their knowledge, simply by placing a call to some recording service.
More subtly, if the exposed APIs allow the server to instruct the More subtly, if the exposed APIs allow the server to instruct the
browser to send arbitrary content, then they can be used to bypass browser to send arbitrary content, then they can be used to bypass
firewalls or mount denial of service attacks. Any successful system firewalls or mount DoS attacks. Any successful system
will need to be resistant to this and other attacks. will need to be resistant to this and other attacks.
</t> </t>
<t> <t>
A companion document <xref target="I-D.ietf-rtcweb-security-arch"/> desc ribes a security A companion document <xref target="RFC8827" format="default"/> describes a security
architecture intended to address the issues raised in this document. architecture intended to address the issues raised in this document.
</t> </t>
</section> </section>
<section anchor="sec-term" title="Terminology"> <section anchor="sec-term" numbered="true" toc="default">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", <name>Terminology</name>
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and <t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"OPTIONAL" in this document are to be interpreted as described in "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only w "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
hen, they appear in all "<bcp14>SHOULD NOT</bcp14>",
capitals, as shown here.</t> "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are
to be interpreted as described in BCP&nbsp;14 <xref target="RFC2119"/>
<xref target="RFC8174"/> when, and only when, they appear in all capitals,
as shown here.</t>
</section> </section>
<section anchor="sec.web-security" numbered="true" toc="default">
<section title="The Browser Threat Model" anchor="sec.web-security"> <name>The Browser Threat Model</name>
<t> <t>
The security requirements for WebRTC follow directly from the The security requirements for WebRTC follow directly from the
requirement that the browser's job is to protect the user. requirement that the browser's job is to protect the user.
Huang et al. <xref target="huang-w2sp"/> summarize the core browser secu Huang et al. <xref target="huang-w2sp" format="default"/> summarize
rity guarantee as: the core browser security guarantee as follows:
</t>
<t>
<list style="hanging">
<t>
Users can safely visit arbitrary web sites and execute scripts provi
ded by those sites.
</t>
</list>
</t> </t>
<t></t> <!-- DNE -->
<ul empty="true">
<li>Users can safely visit arbitrary web sites and execute scripts provide
d by those sites.</li></ul>
<t> <t>
It is important to realize that this includes sites hosting arbitrary ma licious It is important to realize that this includes sites hosting arbitrary ma licious
scripts. The motivation for this requirement is simple: it is trivial fo r attackers scripts. The motivation for this requirement is simple: it is trivial fo r attackers
to divert users to sites of their choice. For instance, an attacker can purchase to divert users to sites of their choice. For instance, an attacker can purchase
display advertisements which direct the user (either automatically or vi a user display advertisements which direct the user (either automatically or vi a user
clicking) to their site, at which point the browser will execute the att acker's clicking) to their site, at which point the browser will execute the att acker's
scripts. Thus, it is important that it be safe to view arbitrarily malic ious pages. scripts. Thus, it is important that it be safe to view arbitrarily malic ious pages.
Of course, browsers inevitably have bugs which cause them to fall short of this Of course, browsers inevitably have bugs which cause them to fall short of this
goal, but any new WebRTC functionality must be designed with the intent to goal, but any new WebRTC functionality must be designed with the intent to
meet this standard. The remainder of this section provides more backgrou nd meet this standard. The remainder of this section provides more backgrou nd
on the existing Web security model. on the existing Web security model.
</t> </t>
<t> <t>
In this model, then, the browser acts as a Trusted Coomputing Base (TCB) both In this model, then, the browser acts as a Trusted Computing Base (TCB) both
from the user's perspective and to some extent from the server's. While HTML from the user's perspective and to some extent from the server's. While HTML
and JavaScript (JS) provided by the server can cause the browser to exec ute a variety of and JavaScript provided by the server can cause the browser to execute a variety of
actions, those scripts operate in a sandbox that isolates them both from actions, those scripts operate in a sandbox that isolates them both from
the user's computer and from each other, as detailed below. the user's computer and from each other, as detailed below.
</t> </t>
<t> <t>
Conventionally, we refer to either web attackers, who are able to induce Conventionally, we refer to either Web attackers, who are able to induce
you to visit their sites but do not control the network, and network you to visit their sites but do not control the network, and network
attackers, who are able to control your network. Network attackers corre attackers, who are able to control your network.
spond
to the <xref target="RFC3552"/> "Internet Threat Model". Note that in so <!-- [rfced] Section 3: Should "network, and" be "network, or," or
me should the word "either" be removed?
cases, a network attacker is also a web attacker, since transport protoc
ols Original:
Conventionally, we refer to either web attackers, who are able to
induce you to visit their sites but do not control the network, and
network attackers, who are able to control your network. -->
Network attackers correspond
to the <xref target="RFC3552" format="default"/> "Internet Threat Model"
. Note that in some
cases, a network attacker is also a Web attacker, since transport protoc
ols
that do not provide integrity protection allow the network to inject tra ffic that do not provide integrity protection allow the network to inject tra ffic
as if they were any communications peer. TLS, and HTTPS in particular, p revent as if they were any communications peer. TLS, and HTTPS in particular, p revent
against these attacks, but when analyzing HTTP connections, we must assu me against these attacks, but when analyzing HTTP connections, we must assu me
that traffic is going to the attacker. that traffic is going to the attacker.
</t> </t>
<section title="Access to Local Resources" anchor="sec.resources"> <section anchor="sec.resources" numbered="true" toc="default">
<name>Access to Local Resources</name>
<t> <t>
While the browser has access to local resources such as keying materia l, While the browser has access to local resources such as keying materia l,
files, the camera, and the microphone, it strictly limits or forbids w eb files, the camera, and the microphone, it strictly limits or forbids W eb
servers from accessing those same resources. For instance, while it is possible servers from accessing those same resources. For instance, while it is possible
to produce an HTML form which will allow file upload, a script cannot do to produce an HTML form which will allow file upload, a script cannot do
so without user consent and in fact cannot even suggest a specific fil e so without user consent and in fact cannot even suggest a specific fil e
(e.g., /etc/passwd); the user must explicitly select the file and cons ent (e.g., /etc/passwd); the user must explicitly select the file and cons ent
to its upload. [Note: in many cases browsers are explicitly designed t o to its upload. (Note: In many cases, browsers are explicitly designed to
avoid dialogs with the semantics of "click here to bypass security che cks", as avoid dialogs with the semantics of "click here to bypass security che cks", as
extensive research <xref target="cranor-wolf"/> shows that users are p extensive research <xref target="cranor-wolf" format="default"/> shows
rone to that users are prone to
consent under such circumstances.] consent under such circumstances.)
</t> </t>
<t> <t>
Similarly, while Flash programs (SWFs) <xref target="SWF"/> can access the camera and microphone, they Similarly, while Flash programs (SWFs) <xref target="SWF" format="defa ult"/> can access the camera and microphone, they
explicitly require that the user consent to that access. In addition, explicitly require that the user consent to that access. In addition,
some resources simply cannot be accessed from the browser at all. For some resources simply cannot be accessed from the browser at all. For
instance, there is no real way to run specific executables directly fr om a instance, there is no real way to run specific executables directly fr om a
script (though the user can of course be induced to download executabl e script (though the user can of course be induced to download executabl e
files and run them). files and run them).
</t> </t>
</section> </section>
<section title="Same-Origin Policy" anchor="sec.same-origin"> <section anchor="sec.same-origin" numbered="true" toc="default">
<name>Same-Origin Policy</name>
<t> <t>
Many other resources are accessible but isolated. For instance, Many other resources are accessible but isolated. For instance,
while scripts are allowed to make HTTP requests via the XMLHttpRequest () API (see <xref target="XmlHttpRequest"/>) while scripts are allowed to make HTTP requests via the XMLHttpRequest () API (see <xref target="XmlHttpRequest" format="default"/>)
those requests are not allowed to be made to any server, but rather so lely those requests are not allowed to be made to any server, but rather so lely
to the same ORIGIN from whence the script came <xref target="RFC6454"/ to the same ORIGIN from whence the script came <xref target="RFC6454"
> format="default"/>
(although CORS <xref target="CORS"/> and WebSockets (although Cross-Origin Resource Sharing (CORS) <xref target="CORS" for
<xref target="RFC6455"/> provide an escape hatch from this restriction mat="default"/> and WebSockets
, <xref target="RFC6455" format="default"/> provide an escape hatch from
as described below.) this restriction,
This SAME ORIGIN POLICY (SOP) prevents server A from mounting attacks as described below).
This SAME-ORIGIN POLICY (SOP) prevents server A from mounting attacks
on server B via the user's browser, which protects both the user on server B via the user's browser, which protects both the user
(e.g., from misuse of his credentials) and the server B (e.g., from (e.g., from misuse of his credentials) and server B (e.g., from
DoS attack). DoS attacks).
<!-- [rfced] Section 3.2: Are "ORIGIN" and "SAME ORIGIN POLICY"
written in all capitals for emphasis (in which case perhaps we
could use the <strong> element (Section 2.50 of RFC 7991)), or should
we write them as "origin" (as used elsewhere in this document and
this cluster) and "Same-Origin Policy" (as used elsewhere in this
document and in several published RFCs)?
Also, per the "Gender-Specific Language" section of
<https://www.rfc-editor.org/styleguide/part2/>, please let us know
if we may change instances of "his," "him," "himself," and "he" to
"their," "them," "themselves," and "they."
Original "(as described below.)" has been fixed):
For instance,
while scripts are allowed to make HTTP requests via the
XMLHttpRequest() API (see [XmlHttpRequest]) those requests are not
allowed to be made to any server, but rather solely to the same
ORIGIN from whence the script came [RFC6454] (although CORS [CORS]
and WebSockets [RFC6455] provide an escape hatch from this
restriction, as described below.) This SAME ORIGIN POLICY (SOP)
prevents server A from mounting attacks on server B via the user's
browser, which protects both the user (e.g., from misuse of his
credentials) and the server B (e.g., from DoS attack). -->
</t> </t>
<t> <t>
More generally, SOP forces scripts from each site to run in their own, isolated, More generally, SOP forces scripts from each site to run in their own, isolated,
sandboxes. While there are techniques to allow them to interact, those interactions sandboxes. While there are techniques to allow them to interact, those interactions
generally must be mutually consensual (by each site) and are limited t o certain generally must be mutually consensual (by each site) and are limited t o certain
channels. For instance, multiple pages/browser panes from the same ori channels. For instance, multiple pages / browser panes from the same o
gin rigin
can read each other's JS variables, but pages from the different origi can read each other's JS variables, but pages from different
ns--or origins -- or
even iframes from different origins on the same page--cannot. even iframes from different origins on the same page -- cannot.
</t> </t>
<!-- TODO: Picture -->
<!-- [rfced] Section 3.3: We found a "TODO: Picture" comment in the
XML file, just after the section title. Is a diagram missing? -->
</section> </section>
<section title="Bypassing SOP: CORS, WebSockets, and consent to communicat <section anchor="sec.cors-etc" numbered="true" toc="default">
e" anchor="sec.cors-etc"> <name>Bypassing SOP: CORS, WebSockets, and Consent to Communicate</name>
<t> <t>
While SOP serves an important security function, it also makes it inco nvenient to While SOP serves an important security function, it also makes it inco nvenient to
write certain classes of applications. In particular, mash-ups, in whi ch a script write certain classes of applications. In particular, mash-ups, in whi ch a script
from origin A uses resources from origin B, can only be achieved via a certain amount of hackery. from origin A uses resources from origin B, can only be achieved via a certain amount of hackery.
The W3C Cross-Origin Resource Sharing (CORS) spec <xref target="CORS"/ > is a response to this The W3C CORS spec <xref target="CORS" format="default"/> is a response to this
demand. In CORS, when a script from origin A executes what would other wise be a forbidden demand. In CORS, when a script from origin A executes what would other wise be a forbidden
cross-origin request, the browser instead contacts the target server t o determine cross-origin request, the browser instead contacts the target server t o determine
whether it is willing to allow cross-origin requests from A. If it is so willing, whether it is willing to allow cross-origin requests from A. If it is so willing,
the browser then allows the request. This consent verification process is designed the browser then allows the request. This consent verification process is designed
to safely allow cross-origin requests. to safely allow cross-origin requests.
</t> </t>
<t> <t>
While CORS is designed to allow cross-origin HTTP requests, WebSockets <xref target="RFC6455"/> allows While CORS is designed to allow cross-origin HTTP requests, WebSockets <xref target="RFC6455" format="default"/> allows
cross-origin establishment of transparent channels. Once a WebSockets connection cross-origin establishment of transparent channels. Once a WebSockets connection
has been established from a script to a site, the script can exchange any traffic it has been established from a script to a site, the script can exchange any traffic it
likes without being required to frame it as a series of HTTP request/r esponse likes without being required to frame it as a series of HTTP request/r esponse
transactions. As with CORS, a WebSockets transaction starts with a con sent verification transactions. As with CORS, a WebSockets transaction starts with a con sent verification
stage to avoid allowing scripts to simply send arbitrary data to anoth er origin. stage to avoid allowing scripts to simply send arbitrary data to anoth er origin.
</t> </t>
<t> <t>
While consent verification is conceptually simple--just do a handshake While consent verification is conceptually simple -- just do a handsha
before you ke before you
start exchanging the real data--experience has shown that designing a start exchanging the real data -- experience has shown that designing
correct consent verification system is difficult. In particular, Huang a
et al. <xref target="huang-w2sp"/> correct consent verification system is difficult. In particular, Huang
et al. <xref target="huang-w2sp" format="default"/>
have shown vulnerabilities in the existing Java and Flash consent veri fication have shown vulnerabilities in the existing Java and Flash consent veri fication
techniques and in a simplified version of the WebSockets handshake. In particular, techniques and in a simplified version of the WebSockets handshake. In particular,
it is important to be wary of CROSS-PROTOCOL attacks in which the atta cking script it is important to be wary of CROSS-PROTOCOL attacks in which the atta cking script
generates traffic which is acceptable to some non-Web protocol state m achine. generates traffic which is acceptable to some non-Web protocol state m achine.
In order to resist this form of attack, WebSockets incorporates a mask ing technique In order to resist this form of attack, WebSockets incorporates a mask ing technique
intended to randomize the bits on the wire, thus making it more diffic ult to generate intended to randomize the bits on the wire, thus making it more diffic ult to generate
traffic which resembles a given protocol. traffic which resembles a given protocol.
</t> </t>
</section> </section>
</section> </section>
<section anchor="sec.rtc-web" numbered="true" toc="default">
<section title="Security for WebRTC Applications" anchor="sec.rtc-web"> <name>Security for WebRTC Applications</name>
<section title="Access to Local Devices" anchor="sec.rtc-dev-access"> <section anchor="sec.rtc-dev-access" numbered="true" toc="default">
<name>Access to Local Devices</name>
<t> <t>
As discussed in <xref target="sec.introduction"/>, allowing arbitrary As discussed in <xref target="sec.introduction" format="default"/>, al lowing arbitrary
sites to initiate calls violates the core Web security guarantee; sites to initiate calls violates the core Web security guarantee;
without some access restrictions on local devices, any malicious site without some access restrictions on local devices, any malicious site
could simply bug a user. At minimum, then, it MUST NOT be possible for could simply bug a user. At minimum, then, it <bcp14>MUST NOT</bcp14> be possible for
arbitrary sites to initiate calls to arbitrary locations without user arbitrary sites to initiate calls to arbitrary locations without user
consent. This immediately raises the question, however, of what should consent. This immediately raises the question, however, of what should
be the scope of user consent. be the scope of user consent.
</t> </t>
<t> <t>
In order for the user to In order for the user to
make an intelligent decision about whether to allow a call make an intelligent decision about whether to allow a call
(and hence his camera and microphone input to be routed somewhere), (and hence his camera and microphone input to be routed somewhere),
he must understand either who is requesting access, where the media he must understand who is requesting access, where the media
is going, or both. As detailed below, there are two basic conceptual is going, or both. As detailed below, there are two basic conceptual
models: models:
</t> </t>
<t> <ol spacing="normal" type="1">
<list style="numbers"> <li>You are sending your media to entity A because you want to
<t>You are sending your media to entity A because you want to talk to entity A (e.g., your mother).</li>
talk to Entity A (e.g., your mother).</t> <li>Entity A (e.g., a calling service) asks to access the user's devic
<t>Entity A (e.g., a calling service) asks to access the user's devi es with the assurance
ces with the assurance that it will transfer the media to entity B (e.g., your mother).</li
that it will transfer the media to entity B (e.g., your mother)</t> >
</list> </ol>
</t>
<t> <t>
In either case, identity is at the heart of any consent decision. In either case, identity is at the heart of any consent decision.
Moreover, the identity of the party the browser is connecting to is al l that the browser can meaningfully enforce; Moreover, the identity of the party the browser is connecting to is al l that the browser can meaningfully enforce;
if you are calling A, A can simply forward the media to C. Similarly, if you are calling A, A can simply forward the media to C. Similarly,
if you authorize A to place a call to B, A can call C instead. if you authorize A to place a call to B, A can call C instead.
In either cases, all the browser is able to do is verify and check In either case, all the browser is able to do is verify and check
authorization for whoever is controlling where the media goes. authorization for whoever is controlling where the media goes.
The target of the media can of course advertise a security/privacy The target of the media can of course advertise a security/privacy
policy, but this is not something that the browser can policy, but this is not something that the browser can
enforce. Even so, there are a variety of different consent scenarios enforce. Even so, there are a variety of different consent scenarios
that motivate different technical consent mechanisms. that motivate different technical consent mechanisms.
We discuss these mechanisms in the sections below. We discuss these mechanisms in the sections below.
</t> </t>
<t> <t>
It's important to understand that consent to access local devices It's important to understand that consent to access local devices
is largely orthogonal to consent to transmit various kinds of is largely orthogonal to consent to transmit various kinds of
data over the network (see <xref target="sec.rtc-comm-consent"/>). data over the network (see <xref target="sec.rtc-comm-consent" format= "default"/>).
Consent for device access is largely a matter of protecting Consent for device access is largely a matter of protecting
the user's privacy from malicious sites. By contrast, the user's privacy from malicious sites. By contrast,
consent to send network traffic is about preventing the consent to send network traffic is about preventing the
user's browser from being used to attack its local network. user's browser from being used to attack its local network.
Thus, we need to ensure communications consent even if the Thus, we need to ensure communications consent even if the
site is not able to access the camera and microphone at site is not able to access the camera and microphone at
all (hence WebSockets's consent mechanism) and similarly all (hence WebSockets's consent mechanism); similarly,
we need to be concerned with the site accessing the we need to be concerned with the site accessing the
user's camera and microphone even if the data is to be user's camera and microphone even if the data is to be
sent back to the site via conventional HTTP-based network sent back to the site via conventional HTTP-based network
mechanisms such as HTTP POST. mechanisms such as HTTP POST.
</t> </t>
<section title="Threats from Screen Sharing"> <section numbered="true" toc="default">
<name>Threats from Screen Sharing</name>
<t> <t>
In addition to camera and microphone access, there has been In addition to camera and microphone access, there has been
demand for screen and/or application sharing functionality. demand for screen and/or application sharing functionality.
Unfortunately, the security implications of this Unfortunately, the security implications of this
functionality are much harder for users to intuitively functionality are much harder for users to intuitively
analyze than for camera and microphone access. analyze than for camera and microphone access.
(See http://lists.w3.org/Archives/Public/public-webrtc/2013Mar/0024. html (See <eref brackets="angle" target="https://lists.w3.org/Archives/Pu blic/public-webrtc/2013Mar/0024.html"/>
for a full analysis.) for a full analysis.)
</t> </t>
<t> <t>
The most obvious threats are simply those of "oversharing". The most obvious threats are simply those of "oversharing".
I.e., the user may believe they are sharing a window when That is, the user may believe they are sharing a window when
in fact they are sharing an application, or may forget they in fact they are sharing an application, or may forget they
are sharing their whole screen, icons, notifications, and all. are sharing their whole screen, icons, notifications, and all.
This is already an issue with existing screen sharing technologies This is already an issue with existing screen sharing technologies
and is made somewhat worse if a partially trusted site is responsibl e for asking and is made somewhat worse if a partially trusted site is responsibl e for asking
for the resource to be shared rather than having the user propose it . for the resource to be shared rather than having the user propose it .
</t> </t>
<t> <t>
A less obvious threat involves the impact of screen sharing on the A less obvious threat involves the impact of screen sharing on the
Web security model. A key part of the Same-Origin Policy is that Web security model. A key part of the Same-Origin Policy is that
HTML or JS from site A can reference content from site B and cause HTML or JS from site A can reference content from site B and cause
the browser to load it, but (unless explicitly permitted) cannot the browser to load it, but (unless explicitly permitted) cannot
see the result. However, if a web application from a site is see the result. However, if a Web application from a site is
screen sharing the browser, then this violates that invariant, screen sharing the browser, then this violates that invariant,
with serious security consequences. For example, an attacker site with serious security consequences. For example, an attacker site
might request screen sharing and then briefly open up a new might request screen sharing and then briefly open up a new
Window to the user's bank or webmail account, using screen sharing window to the user's bank or webmail account, using screen sharing
to read the resulting displayed content. A more sophisticated to read the resulting displayed content. A more sophisticated
attack would be open up a source view window to a site and use the attack would be to open up a source view window to a site and use th
screen sharing result to view anti cross-site request forgery tokens e
. screen sharing result to view anti-cross-site request forgery tokens
.
</t> </t>
<t> <t>
These threats suggest that screen/application sharing might need These threats suggest that screen/application sharing might need
a higher level of user consent than access to the camera or a higher level of user consent than access to the camera or
microphone. microphone.
</t> </t>
</section> </section>
<section title="Calling Scenarios and User Expectations"> <section numbered="true" toc="default">
<name>Calling Scenarios and User Expectations</name>
<t> <t>
While a large number of possible calling scenarios are possible, the While a large number of possible calling scenarios are possible, the
scenarios discussed in this section illustrate many of scenarios discussed in this section illustrate many of
the difficulties of identifying the relevant scope of consent. the difficulties of identifying the relevant scope of consent.
</t> </t>
<section title="Dedicated Calling Services"> <section numbered="true" toc="default">
<name>Dedicated Calling Services</name>
<t> <t>
The first scenario we consider is a dedicated calling service. In this The first scenario we consider is a dedicated calling service. In this
case, the user has a relationship with a calling site case, the user has a relationship with a calling site
and repeatedly makes calls on it. It is likely and repeatedly makes calls on it. It is likely
that rather than having to give permission for each call that rather than having to give permission for each call,
that the user will want to give the calling service long-term the user will want to give the calling service long-term
access to the camera and microphone. This is a natural fit access to the camera and microphone. This is a natural fit
for a long-term consent mechanism (e.g., installing an for a long-term consent mechanism (e.g., installing an
app store "application" to indicate permission for the app store "application" to indicate permission for the
calling service.) calling service).
A variant of the dedicated calling service is a gaming site A variant of the dedicated calling service is a gaming site
(e.g., a poker site) which hosts a dedicated calling service (e.g., a poker site) which hosts a dedicated calling service
to allow players to call each other. to allow players to call each other.
</t> </t>
<t> <t>
With any kind of service where the user may use the same With any kind of service where the user may use the same
service to talk to many different people, there is a question service to talk to many different people, there is a question
about whether the user can know who they are talking to. about whether the user can know who they are talking to.
If I grant permission to calling service A to make calls If I grant permission to calling service A to make calls
on my behalf, then I am implicitly granting it permission on my behalf, then I am implicitly granting it permission
to bug my computer whenever it wants. This suggests another to bug my computer whenever it wants. This suggests another
consent model in which a site is authorized to make calls consent model in which a site is authorized to make calls
but only to certain target entities (identified via but only to certain target entities (identified via
media-plane cryptographic mechanisms as described in media-plane cryptographic mechanisms as described in
<xref target="sec.during-attack"/> and especially <xref target="sec.during-attack" format="default"/> and especially
<xref target="sec.third-party-id"/>.) Note that the <xref target="sec.third-party-id" format="default"/>). Note that t
he
question of consent here is related to but question of consent here is related to but
distinct from the question of peer identity: I distinct from the question of peer identity: I
might be willing to allow a calling site to in general might be willing to allow a calling site to in general
initiate calls on my behalf but still have some calls initiate calls on my behalf but still have some calls
via that site where I can be sure that the site is not via that site where I can be sure that the site is not
listening in. listening in.
</t> </t>
</section> </section>
<section title="Calling the Site You're On"> <section numbered="true" toc="default">
<name>Calling the Site You're On</name>
<t> <t>
Another simple scenario is calling the site you're actually visiti ng. Another simple scenario is calling the site you're actually visiti ng.
The paradigmatic case here is the "click here to talk to a The paradigmatic case here is the "click here to talk to a
representative" windows that appear on many shopping sites. representative" windows that appear on many shopping sites.
In this case, the user's expectation is that they are In this case, the user's expectation is that they are
calling the site they're actually visiting. However, it is calling the site they're actually visiting. However, it is
unlikely that they want to provide a general consent to such unlikely that they want to provide a general consent to such
a site; just because I want some information on a car a site; just because I want some information on a car
doesn't mean that I want the car manufacturer to be able doesn't mean that I want the car manufacturer to be able
to activate my microphone whenever they please. Thus, to activate my microphone whenever they please. Thus,
this suggests the need for a second consent mechanism this suggests the need for a second consent mechanism
where I only grant consent for the duration of a given where I only grant consent for the duration of a given
call. As described in <xref target="sec.resources"/>, call. As described in <xref target="sec.resources" format="default "/>,
great care must be taken in the design of this interface great care must be taken in the design of this interface
to avoid the users just clicking through. Note also to avoid the users just clicking through. Note also
that the user interface chrome, which is the representation that the user interface chrome, which is the representation
through which the user interacts with the user agent itself, through which the user interacts with the user agent itself,
must clearly display elements must clearly display elements
showing that the call is continuing in order to avoid attacks showing that the call is continuing in order to avoid attacks
where the calling site just leaves it up indefinitely but where the calling site just leaves it up indefinitely but
shows a Web UI that implies otherwise. shows a Web UI that implies otherwise.
</t> </t>
</section> </section>
</section> </section>
<section title="Origin-Based Security"> <section numbered="true" toc="default">
<t> <name>Origin-Based Security</name>
<t>
Now that we have described the calling scenarios, we can start to reas on about Now that we have described the calling scenarios, we can start to reas on about
the security requirements. the security requirements.
</t> </t>
<t> <t>
As discussed in <xref target="sec.same-origin"/>, the basic unit of As discussed in <xref target="sec.same-origin" format="default"/>, the
basic unit of
Web sandboxing is the origin, and so it is natural to scope consent Web sandboxing is the origin, and so it is natural to scope consent
to origin. Specifically, a script from origin A MUST only be allowed to the origin. Specifically, a script from origin A <bcp14>MUST</bcp14
to initiate communications (and hence to access camera and microphone) > only be allowed
to initiate communications (and hence to access the camera and microph
one)
if the user has specifically authorized access for that origin. if the user has specifically authorized access for that origin.
It is of course technically possible to have coarser-scoped permission s, It is of course technically possible to have coarser-scoped permission s,
but because the Web model is scoped to origin, this creates a difficul t but because the Web model is scoped to the origin, this creates a diff icult
mismatch. mismatch.
</t> </t>
<t> <t>
Arguably, origin is not fine-grained enough. Consider the situation wh Arguably, the origin is not fine-grained enough. Consider the situatio
ere n where
Alice visits a site and authorizes it to make a single call. If consen t is Alice visits a site and authorizes it to make a single call. If consen t is
expressed solely in terms of origin, then at any future visit to that expressed solely in terms of the origin, then upon any future visit to
site (including one induced via mash-up or ad network), the site can that
site (including one induced via a mash-up or ad network), the site can
bug Alice's computer, use the computer to place bogus calls, etc. bug Alice's computer, use the computer to place bogus calls, etc.
While in principle Alice could grant and then While in principle Alice could grant and then
revoke the privilege, in practice privileges accumulate; if we are con cerned revoke the privilege, in practice privileges accumulate; if we are con cerned
about this attack, something else is needed. There are a number of pot ential countermeasures to about this attack, something else is needed. There are a number of pot ential countermeasures to
this sort of issue. this sort of issue.
</t> </t>
<t><list style="hanging"> <dl newline="true" spacing="normal">
<t hangText="Individual Consent"></t><t>Ask the user for permission fo <dt>Individual Consent</dt>
r each call.</t> <dd>Ask the user for permission for each call.</dd>
<t></t> <dt>Callee-oriented Consent</dt>
<t hangText="Callee-oriented Consent"></t><t>Only allow calls to a giv <dd>Only allow calls to a given user.</dd>
en user.</t> <dt>Cryptographic Consent</dt>
<t></t> <dd>Only allow calls to a given set of peer keying material or
<t hangText="Cryptographic Consent"></t><t>Only allow calls to a given to a cryptographically established identity.</dd>
set of peer keying material or </dl>
to a cryptographically established identity.</t> <t>
</list>
</t>
<t>
Unfortunately, none of these approaches is satisfactory for all cases. Unfortunately, none of these approaches is satisfactory for all cases.
As discussed above, individual consent puts the user's approval As discussed above, individual consent puts the user's approval
in the UI flow for every call. Not only does this quickly become annoy ing in the UI flow for every call. Not only does this quickly become annoy ing
but it can train the user to simply click "OK", at which point the con sent becomes but it can train the user to simply click "OK", at which point the con sent becomes
useless. Thus, while it may be necessary to have individual consent in some useless. Thus, while it may be necessary to have individual consent in some
case, this is not a suitable solution for (for instance) the calling cases, this is not a suitable solution for (for instance) the calling
service case. Where necessary, in-flow user interfaces must be careful ly service case. Where necessary, in-flow user interfaces must be careful ly
designed to avoid the risk of the user blindly clicking through. designed to avoid the risk of the user blindly clicking through.
</t> </t>
<t> <t>
The other two options are designed to restrict calls to a given target . The other two options are designed to restrict calls to a given target .
Callee-oriented consent provided by the calling site Callee-oriented consent provided by the calling site
would not work well because a malicious site can claim that the would not work well because a malicious site can claim that the
user is calling any user of his choice. One fix for this is to tie cal ls to a user is calling any user of his choice. One fix for this is to tie cal ls to a
cryptographically-established identity. While not suitable for all cas es, cryptographically established identity. While not suitable for all cas es,
this approach may be useful for some. If we consider the case this approach may be useful for some. If we consider the case
of advertising, it's not particularly convenient of advertising, it's not particularly convenient
to require the advertiser to instantiate an iframe on the hosting site just to require the advertiser to instantiate an iframe on the hosting site just
to get permission; a more convenient approach is to cryptographically tie to get permission; a more convenient approach is to cryptographically tie
the advertiser's certificate to the communication directly. We're stil l the advertiser's certificate to the communication directly. We're stil l
tying permissions to origin here, but to the media origin (and-or dest tying permissions to the origin here, but to the media origin (and/or
ination) destination)
rather than to the Web origin. <xref target="I-D.ietf-rtcweb-security- rather than to the Web origin. <xref target="RFC8827" format="default"
arch"/> />
describes mechanisms describes mechanisms which facilitate this sort of consent.
which facilitate this sort of consent. </t>
</t> <t>
<t>
Another case where media-level cryptographic identity makes sense is w hen a user Another case where media-level cryptographic identity makes sense is w hen a user
really does not trust the calling site. For instance, I might be worri ed that really does not trust the calling site. For instance, I might be worri ed that
the calling service will attempt to bug my computer, but I also want t o be the calling service will attempt to bug my computer, but I also want t o be
able to conveniently call my friends. If consent is tied to particular able to conveniently call my friends. If consent is tied to particular
communications endpoints, then my risk is limited. Naturally, it communications endpoints, then my risk is limited. Naturally, it
is somewhat challenging to design UI primitives which express this sor t is somewhat challenging to design UI primitives that express this sort
of policy. The problem becomes even more challenging in multi-user of policy. The problem becomes even more challenging in multi-user
calling cases. calling cases.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Security Properties of the Calling Page"> <name>Security Properties of the Calling Page</name>
<t> <t>
Origin-based security is intended to secure against web attackers. How Origin-based security is intended to secure against Web attackers. How
ever, we must ever, we must
also consider the case of network attackers. Consider the case where I have also consider the case of network attackers. Consider the case where I have
granted permission to a calling service by an origin that has the HTTP scheme, granted permission to a calling service by an origin that has the HTTP scheme,
e.g., http://calling-service.example.com. If I ever use my computer on e.g., &lt;http://calling-service.example.com&gt;. If I ever use my com puter on
an unsecured network (e.g., a hotspot or if my own home wireless netwo rk an unsecured network (e.g., a hotspot or if my own home wireless netwo rk
is insecure), and browse any HTTP site, then an attacker can bug my co mputer. The attack proceeds is insecure), and browse any HTTP site, then an attacker can bug my co mputer. The attack proceeds
like this: like this:
</t> </t>
<t> <ol spacing="normal" type="1">
<list style="numbers"> <li>I connect to &lt;http://anything.example.org/&gt;. Note that thi
<t>I connect to http://anything.example.org/. Note that this site is s site is unaffiliated
unaffiliated with the calling service.</li>
with the calling service.</t> <li>The attacker modifies my HTTP connection to inject an IFRAME (or
<t>The attacker modifies my HTTP connection to inject an IFRAME (or a redirect)
a redirect) to &lt;http://calling-service.example.com&gt;.</li>
to http://calling-service.example.com</t> <li>The attacker forges the response from &lt;http://calling-service
<t>The attacker forges the response from http://calling-service.exa .example.com/&gt; to
mple.com/ to inject JS to initiate a call to himself.</li>
inject JS to initiate a call to himself.</t> </ol>
</list>
</t> <t>
<t>
Note that this attack does not depend on the media being insecure. Bec ause the Note that this attack does not depend on the media being insecure. Bec ause the
call is to the attacker, it is also encrypted to him. Moreover, it nee d not call is to the attacker, it is also encrypted to him. Moreover, it nee d not
be executed immediately; the attacker can "infect" the origin semi-per manently be executed immediately; the attacker can "infect" the origin semi-per manently
(e.g., with a web worker or a popped-up window that is hidden under th e main window.) (e.g., with a Web worker or a popped-up window that is hidden under th e main window)
and thus be able to bug me long and thus be able to bug me long
after I have left the infected network. This risk is created by allowi ng after I have left the infected network. This risk is created by allowi ng
calls at all from a page fetched over HTTP. calls at all from a page fetched over HTTP.
</t> </t>
<t> <t>
Even if calls are only possible from HTTPS [RFC2818] sites, Even if calls are only possible from HTTPS <xref target="RFC2818" form
at="default"/> sites,
if those sites include active content (e.g., JavaScript) from an untru sted if those sites include active content (e.g., JavaScript) from an untru sted
site, that JavaScript is executed in the security context of the page site, that JavaScript is executed in the security context of the page
<xref target="finer-grained"/>. This could lead to compromise of a cal <xref target="finer-grained" format="default"/>. This could lead to co
l mpromise of a call
even if the parent page is safe. Note: this issue is not restricted even if the parent page is safe. Note: This issue is not restricted
to PAGES which contain untrusted content. If any page from a to PAGES which contain untrusted content.
<!-- [rfced] Section 4.1.4: Is "PAGES" capped for emphasis, or
should it be "pages"? (We see "a page" and "the page" used in nearby
text in this section.) If emphasis is desired, perhaps we could use
the <strong> element (Section 2.50 of RFC 7991) here.
Original:
Note: this issue is not restricted to PAGES
which contain untrusted content. -->
If any page from a
given origin ever loads JavaScript from an attacker, then it is given origin ever loads JavaScript from an attacker, then it is
possible for that attacker to infect the browser's notion of that possible for that attacker to infect the browser's notion of that
origin semi-permanently. origin semi-permanently.
</t> </t>
</section> </section>
</section> </section>
<section anchor="sec.rtc-comm-consent" numbered="true" toc="default">
<section title="Communications Consent Verification" anchor="sec.rtc-comm- <name>Communications Consent Verification</name>
consent">
<t> <t>
As discussed in <xref target="sec.cors-etc"/>, allowing web applicatio ns unrestricted network access As discussed in <xref target="sec.cors-etc" format="default"/>, allowi ng Web applications unrestricted network access
via the browser introduces the risk of using the browser as an attack platform against via the browser introduces the risk of using the browser as an attack platform against
machines which would not otherwise be accessible to the malicious site machines which would not otherwise be accessible to the malicious
, for site -- for
instance because they are topologically restricted (e.g., behind a fir instance, because they are topologically restricted (e.g., behind a fi
ewall or NAT). rewall or NAT).
In order to prevent this form of attack as well as cross-protocol atta In order to prevent this form of attack as well as cross-protocol atta
cks it is cks, it is
important to require that the target of traffic explicitly consent to receiving important to require that the target of traffic explicitly consent to receiving
the traffic in question. Until that consent has been verified for a gi ven endpoint, the traffic in question. Until that consent has been verified for a gi ven endpoint,
traffic other than the consent handshake MUST NOT be sent to that endp oint. traffic other than the consent handshake <bcp14>MUST NOT</bcp14> be se nt to that endpoint.
</t> </t>
<t> <t>
Note that consent verification is not sufficient to prevent overuse of Note that consent verification is not sufficient to prevent overuse of
network resources. Because WebRTC allows for a Web site to create network resources. Because WebRTC allows for a Web site to create
data flows between two browser instances without user consent, it is data flows between two browser instances without user consent, it is
possible for a malicious site to chew up a significant amount of a use r's possible for a malicious site to chew up a significant amount of a use r's
bandwidth without incurring significant costs to himself by setting bandwidth without incurring significant costs to himself by setting
up such a channel to another user. However, as a practical matter up such a channel to another user. However, as a practical matter
there are a large number of Web sites which can act as data sources, there are a large number of Web sites which can act as data sources,
so an attacker can at least use downlink bandwidth with existing so an attacker can at least use downlink bandwidth with existing
Web APIs. However, this potential DoS vector reinforces the need Web APIs. However, this potential DoS vector reinforces the need
for adequate congestion control for WebRTC protocols to ensure that for adequate congestion control for WebRTC protocols to ensure that
they play fair with other demands on the user's bandwidth. they play fair with other demands on the user's bandwidth.
</t> </t>
<section title="ICE" anchor="sec.ice"> <section anchor="sec.ice" numbered="true" toc="default">
<name>ICE</name>
<t> <t>
Verifying receiver consent requires some sort of explicit handshake, b ut conveniently Verifying receiver consent requires some sort of explicit handshake, b ut conveniently
we already need one in order to do NAT hole-punching. Interactive Conn ectivity Establishment (ICE) <xref target="RFC8445"/> includes a handshake we already need one in order to do NAT hole-punching. Interactive Conn ectivity Establishment (ICE) <xref target="RFC8445" format="default"/> includes a handshake
designed to verify that the receiving element wishes to receive traffi c from the designed to verify that the receiving element wishes to receive traffi c from the
sender. It sender. It
is important to remember here that the site initiating ICE is is important to remember here that the site initiating ICE is
presumed malicious; in order for the handshake to be secure the presumed malicious; in order for the handshake to be secure, the
receiving element MUST demonstrate receipt/knowledge of some value receiving element <bcp14>MUST</bcp14> demonstrate receipt/knowledge of
some value
not available to the site (thus preventing the site from forging not available to the site (thus preventing the site from forging
responses). In order to achieve this objective with ICE, the STUN responses). In order to achieve this objective with ICE, the
transaction IDs must be generated by the browser and MUST NOT be made Session Traversal Utilities for NAT (STUN)
transaction IDs must be generated by the browser and <bcp14>MUST NOT</
bcp14> be made
available to the initiating script, even via a diagnostic interface. available to the initiating script, even via a diagnostic interface.
Verifying receiver consent also requires verifying the receiver wants Verifying receiver consent also requires verifying the receiver wants
to receive traffic from a particular sender, and at this time; for to receive traffic from a particular sender, and at this time; for
example a malicious site may simply attempt ICE to known servers example, a malicious site may simply attempt ICE to known servers
that are using ICE for other sessions. ICE provides this verification that are using ICE for other sessions. ICE provides this verification
as well, by using the STUN credentials as a form of per-session shared as well, by using the STUN credentials as a form of per-session shared
secret. Those credentials are known to the Web application, but would secret. Those credentials are known to the Web application, but would
need to also be known and used by the STUN-receiving element to be use ful. need to also be known and used by the STUN-receiving element to be use ful.
</t> </t>
<t> <t>
There also needs to be some mechanism for the browser to verify that There also needs to be some mechanism for the browser to verify that
the target of the traffic continues to wish to receive it. Because I CE keepalives are the target of the traffic continues to wish to receive it. Because I CE keepalives are
indications, they will not work here. indications, they will not work here.
<xref target="RFC7675"/> describes the mechanism <xref target="RFC7675" format="default"/> describes the mechanism
for providing consent freshness. for providing consent freshness.
</t> </t>
</section> </section>
<section title="Masking" anchor="sec.masking"> <section anchor="sec.masking" numbered="true" toc="default">
<name>Masking</name>
<t> <t>
Once consent is verified, there still is some concern about misinter pretation Once consent is verified, there still is some concern about misinter pretation
attacks as described by Huang et al.<xref target="huang-w2sp"/>. attacks as described by Huang et al. <xref target="huang-w2sp" forma
Where TCP is used the risk is substantial due to the potential t="default"/>.
presence of transparent proxies and therefore if TCP is to be used, Where TCP is used, the risk is substantial due to the potential
then WebSockets style masking MUST be employed. presence of transparent proxies; therefore, if TCP is to be used,
then WebSockets-style masking <bcp14>MUST</bcp14> be employed.
</t> </t>
<t> <t>
Since DTLS (with the anti-chosen plaintext mechanisms required by Since DTLS (with the anti-chosen plaintext mechanisms required by
TLS 1.1) does not allow the attacker to generate predictable TLS 1.1) does not allow the attacker to generate predictable
ciphertext, there is no need for masking of protocols running over ciphertext, there is no need for masking of protocols running over
DTLS (e.g. SCTP over DTLS, UDP over DTLS, etc.). DTLS (e.g., SCTP over DTLS, UDP over DTLS, etc.).
</t> </t>
<t> <t>
Note that in principle an attacker could exert some control Note that in principle an attacker could exert some control
over SRTP packets by using a combination of the WebAudio API over Secure Real-time Transport Protocol (SRTP) packets by using a c ombination of the WebAudio API
and extremely tight timing control. and extremely tight timing control.
The primary risk here seems to be carriage of SRTP over TURN TCP. The primary risk here seems to be carriage of SRTP over Traversal
Using Relays around NAT (TURN) TCP.
However, as SRTP packets have an extremely characteristic packet However, as SRTP packets have an extremely characteristic packet
header it seems unlikely that any but the most aggressive header it seems unlikely that any but the most aggressive
intermediaries would be confused into thinking that another intermediaries would be confused into thinking that another
application layer protocol was in use. application-layer protocol was in use.
</t> </t>
</section> </section>
<section title="Backward Compatibility"> <section numbered="true" toc="default">
<name>Backward Compatibility</name>
<t> <t>
A requirement to use ICE limits compatibility with legacy non-ICE cl ients. A requirement to use ICE limits compatibility with legacy non-ICE cl ients.
It seems unsafe to completely remove the requirement for some check. It seems unsafe to completely remove the requirement for some check.
All proposed checks have the common feature that the browser All proposed checks have the common feature that the browser
sends some message to the candidate traffic recipient sends some message to the candidate traffic recipient
and refuses to send other traffic until that message has been and refuses to send other traffic until that message has been
replied to. The message/reply pair must be generated in such replied to. The message/reply pair must be generated in such
a way that an attacker who controls the Web application a way that an attacker who controls the Web application
cannot forge them, generally by having the message contain some cannot forge them, generally by having the message contain some
secret value that must be incorporated (e.g., echoed, hashed into, secret value that must be incorporated (e.g., echoed, hashed into,
etc.). Non-ICE candidates for this role (in cases where the etc.). Non-ICE candidates for this role (in cases where the
legacy endpoint has a public address) include: legacy endpoint has a public address) include:
</t> </t>
<t> <ul spacing="normal">
<list style="symbols"> <li>STUN checks without using ICE (i.e., the non-RTC-web endpoint se
<t>STUN checks without using ICE (i.e., the non-RTC-web endpoint s ts up a STUN responder).</li>
ets up a STUN responder.)</t> <li>Use of the RTP Control Protocol (RTCP) as an implicit reachabili
<t>Use of RTCP as an implicit reachability check.</t> ty check.</li>
</list> </ul>
</t>
<t> <t>
In the RTCP approach, the WebRTC endpoint is allowed to send In the RTCP approach, the WebRTC endpoint is allowed to send
a limited number of RTP packets prior to receiving consent. This a limited number of RTP packets prior to receiving consent. This
allows a short window of attack. In addition, some legacy endpoints allows a short window of attack. In addition, some legacy endpoints
do not support RTCP, so this is a much more expensive solution for do not support RTCP, so this is a much more expensive solution for
such endpoints, for which it would likely be easier to implement ICE . such endpoints, for which it would likely be easier to implement ICE .
For these two reasons, an RTCP-based approach does not seem to For these two reasons, an RTCP-based approach does not seem to
address the security issue satisfactorily. address the security issue satisfactorily.
</t> </t>
<t> <t>
skipping to change at line 683 skipping to change at line 714
the recipient is running some kind of STUN endpoint but unless the recipient is running some kind of STUN endpoint but unless
the STUN responder is integrated with the ICE username/password the STUN responder is integrated with the ICE username/password
establishment system, the WebRTC endpoint cannot verify that establishment system, the WebRTC endpoint cannot verify that
the recipient consents to this particular call. This may be an the recipient consents to this particular call. This may be an
issue if existing STUN servers are operated at addresses that issue if existing STUN servers are operated at addresses that
are not able to handle bandwidth-based attacks. Thus, this are not able to handle bandwidth-based attacks. Thus, this
approach does not seem satisfactory either. approach does not seem satisfactory either.
</t> </t>
<t> <t>
If the systems are tightly integrated (i.e., the STUN endpoint respo nds with If the systems are tightly integrated (i.e., the STUN endpoint respo nds with
responses authenticated with ICE credentials) then this issue responses authenticated with ICE credentials), then this issue
does not exist. However, such a design is very close to an ICE-Lite does not exist. However, such a design is very close to an ICE-Lite
implementation (indeed, arguably is one). implementation (indeed, arguably is one).
An intermediate approach would be to have a STUN extension that indi cated An intermediate approach would be to have a STUN extension that indi cated
that one was responding to WebRTC checks but not computing that one was responding to WebRTC checks but not computing
integrity checks based on the ICE credentials. This would allow the integrity checks based on the ICE credentials. This would allow the
use of standalone STUN servers without the risk of confusing them use of standalone STUN servers without the risk of confusing them
with legacy STUN servers. If a non-ICE legacy solution is needed, with legacy STUN servers. If a non-ICE legacy solution is needed,
then this is probably the best choice. then this is probably the best choice.
</t> </t>
<t> <t>
Once initial consent is verified, we also need to verify continuing Once initial consent is verified, we also need to verify continuing
consent, in order to avoid attacks where two people briefly share consent, in order to avoid attacks where two people briefly share
an IP (e.g., behind a NAT in an Internet cafe) and the attacker an IP (e.g., behind a NAT in an Internet cafe) and the attacker
arranges for a large, unstoppable, traffic flow to the arranges for a large, unstoppable, traffic flow to the
network and then leaves. The appropriate technologies here are network and then leaves. The appropriate technologies here are
fairly similar to those for initial consent, though are perhaps fairly similar to those for initial consent, though are perhaps
weaker since the threats are less severe. weaker since the threats are less severe.
</t> </t>
</section> </section>
<section anchor="sec.ip.location" numbered="true" toc="default">
<section title="IP Location Privacy" anchor="sec.ip.location"> <name>IP Location Privacy</name>
<t> <t>
Note that as soon as the callee sends their ICE candidates, the Note that as soon as the callee sends their ICE candidates, the
caller learns the callee's IP addresses. The callee's server reflexi ve caller learns the callee's IP addresses. The callee's server-reflexi ve
address reveals a lot of information about the callee's location. address reveals a lot of information about the callee's location.
<!-- [rfced] Section 4.2.4: Per author feedback for RFC 8839 and per
other documents in this cluster, we hyphenated the term "server
reflexive". Please let us know any objections.
Original:
The callee's server
reflexive address reveals a lot of information about the callee's
location.
Currently:
The callee's server-
reflexive address reveals a lot of information about the callee's
location. -->
In order to avoid tracking, implementations may wish to suppress In order to avoid tracking, implementations may wish to suppress
the start of ICE negotiation until the callee has answered. In the start of ICE negotiation until the callee has answered. In
addition, either side may wish to hide their location from the other addition, either side may wish to hide their location from the other
side entirely by forcing all traffic through a TURN server. side entirely by forcing all traffic through a TURN server.
</t> </t>
<t> <t>
In ordinary operation, the site learns the browser's IP address, In ordinary operation, the site learns the browser's IP address,
though it may be hidden via mechanisms like Tor [http://www.torproj though it may be hidden via mechanisms like Tor <eref
ect.org] or a VPN. brackets="angle" target="https://www.torproject.org"/> or a VPN.
However, because sites can cause the browser to provide However, because sites can cause the browser to provide
IP addresses, this provides a mechanism for sites to learn IP addresses, this provides a mechanism for sites to learn
about the user's network environment even if the user is behind about the user's network environment even if the user is behind
a VPN that masks their IP address. Implementations may wish a VPN that masks their IP address. Implementations may wish
to provide settings which suppress all non-VPN candidates if to provide settings which suppress all non-VPN candidates if
the user is on certain kinds of VPN, especially privacy-oriented the user is on certain kinds of VPN, especially privacy-oriented
systems such as Tor. See <xref target="I-D.ietf-rtcweb-ip-handling "/> systems such as Tor. See <xref target="RFC8828" format="default"/>
for additional information. for additional information.
</t> </t>
</section> </section>
</section> </section>
<section anchor="sec.rtc-comsec" numbered="true" toc="default">
<section title="Communications Security" anchor="sec.rtc-comsec"> <name>Communications Security</name>
<t> <t>
Finally, we consider a problem familiar from the SIP world: communicat ions security. Finally, we consider a problem familiar from the SIP world: communicat ions security.
For obvious reasons, it MUST be possible for the communicating parties to establish For obvious reasons, it <bcp14>MUST</bcp14> be possible for the commun icating parties to establish
a channel which is secure against both message recovery and message mo dification. a channel which is secure against both message recovery and message mo dification.
(See <xref target="RFC5479"/> for more details.) (See <xref target="RFC5479" format="default"/> for more details.)
This service must be provided for both data and voice/video. This service must be provided for both data and voice/video.
Ideally the same security mechanisms would be used for both types of c ontent. Ideally the same security mechanisms would be used for both types of c ontent.
Technology for providing this Technology for providing this
service (for instance, SRTP <xref target="RFC3711"/>, DTLS <xref targe service (for instance, SRTP <xref target="RFC3711" format="default"/>,
t="RFC6347"/> and DTLS <xref target="RFC6347" format="default"/>, and
DTLS-SRTP <xref target="RFC5763"/>) is well understood. However, we mu DTLS-SRTP <xref target="RFC5763" format="default"/>) is well understoo
st d. However, we must
examine this technology in the WebRTC context, where the threat examine this technology in the WebRTC context, where the threat
model is somewhat different. model is somewhat different.
</t> </t>
<t> <t>
In general, it is important to understand that unlike a conventional S IP proxy, In general, it is important to understand that unlike a conventional S IP proxy,
the calling service (i.e., the Web server) controls not only the chann el the calling service (i.e., the Web server) controls not only the chann el
between the communicating endpoints but also the application running o n between the communicating endpoints but also the application running o n
the user's browser. the user's browser.
While in principle it is possible for the browser to cut the calling s ervice While in principle it is possible for the browser to cut the calling s ervice
out of the loop and directly present trusted information (and perhaps get out of the loop and directly present trusted information (and perhaps get
consent), practice in modern browsers is to avoid this whenever possib le. consent), practice in modern browsers is to avoid this whenever possib le.
"In-flow" modal dialogs which require the user to consent to specific "In&nbhy;flow" modal dialogs which
actions are particularly disfavored as human factors research indicate s actions are particularly disfavored as human factors research indicate s
that unless they are made extremely invasive, users simply agree to that unless they are made extremely invasive, users simply agree to
them without actually consciously giving consent. <xref target="abarth -rtcweb"/>. them without actually consciously giving consent <xref target="abarth- rtcweb" format="default"/>.
Thus, nearly all the UI will necessarily be rendered by the Thus, nearly all the UI will necessarily be rendered by the
browser but under control of the calling service. This likely includes the browser but under control of the calling service. This likely includes the
peer's identity information, which, after all, is only meaningful in peer's identity information, which, after all, is only meaningful in
the context of some calling service. the context of some calling service.
</t> </t>
<t> <t>
This limitation does not mean that preventing attack by the calling se rvice This limitation does not mean that preventing attack by the calling se rvice
is completely hopeless. However, we need to distinguish between two is completely hopeless. However, we need to distinguish between two
classes of attack: classes of attack:
</t> </t>
<t><list style="hanging"> <dl newline="true" spacing="normal">
<t hangText="Retrospective compromise of calling service."></t><t>The <dt>Retrospective compromise of calling service:</dt>
calling service <dd>The calling service
is non-malicious during a call but subsequently is compromised and wis hes to is non-malicious during a call but subsequently is compromised and wis hes to
attack an older call (often called a "passive attack")</t> attack an older call (often called a "passive attack").</dd>
<t></t> <dt>During-call attack by calling service:</dt>
<t hangText="During-call attack by calling service."></t><t>The callin <dd>The calling service is compromised
g service is compromised during the call it wishes to attack (often called an "active attack").
during the call it wishes to attack (often called an "active attack"). </dd>
</t> </dl>
</list>
</t>
<t> <t>
Providing security against the former type of attack is practical usin g the Providing security against the former type of attack is practical usin g the
techniques discussed in <xref target="sec.retrospective-compromise"/>. techniques discussed in <xref target="sec.retrospective-compromise" fo rmat="default"/>.
However, it is extremely difficult to prevent a However, it is extremely difficult to prevent a
trusted but malicious calling service from actively attacking a user's calls, trusted but malicious calling service from actively attacking a user's calls,
either by mounting a Man-in-the-Middle (MITM) attack or by diverting t hem entirely. either by mounting a Man-in-the-Middle (MITM) attack or by diverting t hem entirely.
(Note that this attack applies equally to a network attacker if commun ications (Note that this attack applies equally to a network attacker if commun ications
to the calling service are not secured.) We discuss some potential app roaches to the calling service are not secured.) We discuss some potential app roaches
and why they are likely to be impractical in <xref target="sec.during- attack"/>. and why they are likely to be impractical in <xref target="sec.during- attack" format="default"/>.
</t> </t>
<section title="Protecting Against Retrospective Compromise" anchor="sec <section anchor="sec.retrospective-compromise" numbered="true" toc="defa
.retrospective-compromise"> ult">
<name>Protecting against Retrospective Compromise</name>
<t> <t>
In a retrospective attack, the calling service was uncompromised dur ing In a retrospective attack, the calling service was uncompromised dur ing
the call, but that an attacker subsequently wants to recover the con tent of the the call, but an attacker subsequently wants to recover the content of the
call. We assume that the attacker has access to the protected media stream call. We assume that the attacker has access to the protected media stream
as well as having full control of the calling service. as well as full control of the calling service.
</t> </t>
<t> <t>
If the calling service has access to the traffic keying material If the calling service has access to the traffic keying material
(as in SDES <xref target="RFC4568"/>), then retrospective attack (as in SDES <xref target="RFC4568" format="default"/>), then retrosp ective attack
is trivial. is trivial.
This form of attack is particularly serious in the Web context becau
se <!-- [rfced] Section 4.3.1: We would like to expand "SDES" for ease
of the reader. Does SDES refer to "Security Description" here, or perhaps "Sour
ce Description" per
several other documents in this cluster (e.g., RFC-to-be 8852 <draft-ietf-avtext
-rid>)?
Original:
If the calling service has access to the traffic keying material (as
in SDES [RFC4568]), then retrospective attack is trivial. -->
This form of attack is particularly serious in the context of the We
b because
it is standard practice in Web services to run extensive logging and monitoring. Thus, it is highly it is standard practice in Web services to run extensive logging and monitoring. Thus, it is highly
likely that if the traffic key is part of any HTTP request it will b e logged somewhere and thus likely that if the traffic key is part of any HTTP request it will b e logged somewhere and thus
subject to subsequent compromise. It is this consideration that make s an automatic, public key-based subject to subsequent compromise. It is this consideration that make s an automatic, public key-based
key exchange mechanism imperative for WebRTC (this is a good idea fo r any communications key exchange mechanism imperative for WebRTC (this is a good idea fo r any communications
security system) and this mechanism SHOULD provide perfect forward s security system), and this mechanism <bcp14>SHOULD</bcp14> provide P
ecrecy (PFS). erfect Forward Secrecy (PFS).
The signaling channel/calling service can be used to authenticate th The signaling channel / calling service can be used to authenticate
is mechanism. this mechanism.
</t> </t>
<t> <t>
In addition, if end-to-end keying is in used, In addition, if end-to-end keying is used,
the system MUST NOT provide any APIs to extract either long-term the system <bcp14>MUST NOT</bcp14> provide any APIs to extract eithe
r long-term
keying material or to directly access any stored traffic keys. keying material or to directly access any stored traffic keys.
<!-- [rfced] Section 4.3.1: To what does "either" refer in this
sentence?
Original:
In addition, if end-to-end keying is in used, the system MUST NOT
provide any APIs to extract either long-term keying material or to
directly access any stored traffic keys. -->
Otherwise, an attacker who subsequently compromised the calling serv ice Otherwise, an attacker who subsequently compromised the calling serv ice
might be able to use those APIs to recover the traffic keys and thus might be able to use those APIs to recover the traffic keys and thus
compromise the traffic. compromise the traffic.
</t> </t>
</section> </section>
<section title="Protecting Against During-Call Attack" anchor="sec.durin <section anchor="sec.during-attack" numbered="true" toc="default">
g-attack"> <name>Protecting against During-Call Attack</name>
<t> <t>
Protecting against attacks during a call is a more difficult proposi tion. Even Protecting against attacks during a call is a more difficult proposi tion. Even
if the calling service cannot directly access keying material (as re commended if the calling service cannot directly access keying material (as re commended
in the previous section), it can simply mount a man-in-the-middle at tack in the previous section), it can simply mount a man-in-the-middle at tack
on the connection, telling Alice that she is calling Bob and Bob tha t on the connection, telling Alice that she is calling Bob and Bob tha t
he is calling Alice, while in fact the calling service is acting as he is calling Alice, while in fact the calling service is acting as
a calling bridge and capturing all the traffic. Protecting against a calling bridge and capturing all the traffic. Protecting against
this form of attack requires positive authentication of the remote this form of attack requires positive authentication of the remote
endpoint such as explicit out-of-band key verification (e.g., by a f ingerprint) endpoint such as explicit out-of-band key verification (e.g., by a f ingerprint)
or a third-party identity service as described in or a third-party identity service as described in
<xref target="I-D.ietf-rtcweb-security-arch"/>. <xref target="RFC8827" format="default"/>.
</t> </t>
<section title="Key Continuity" anchor="sec.key-continuity"> <section anchor="sec.key-continuity" numbered="true" toc="default">
<name>Key Continuity</name>
<t> <t>
One natural approach is to use "key continuity". While a malicious One natural approach is to use "key continuity". While a malicious
calling service can present any identity it chooses to the user, calling service can present any identity it chooses to the user,
it cannot produce a private key that maps to a given public key. it cannot produce a private key that maps to a given public key.
Thus, it is possible for the browser to note a given user's Thus, it is possible for the browser to note a given user's
public key and generate an alarm whenever that user's key public key and generate an alarm whenever that user's key
changes. SSH <xref target="RFC4251"/> uses a similar technique. changes. The Secure Shell (SSH) protocol <xref target="RFC4251" fo rmat="default"/> uses a similar technique.
(Note that the need to avoid explicit user consent on every call (Note that the need to avoid explicit user consent on every call
precludes the browser requiring an immediate manual check of the p eer's key). precludes the browser requiring an immediate manual check of the p eer's key.)
</t> </t>
<t> <t>
Unfortunately, this sort of key continuity mechanism is far less Unfortunately, this sort of key continuity mechanism is far less
useful in the WebRTC context. First, much of the virtue of useful in the WebRTC context. First, much of the virtue of
WebRTC (and any Web application) is that it is not bound to WebRTC (and any Web application) is that it is not bound to a
particular piece of client software. Thus, it will be not only particular piece of client software. Thus, it will be not only
possible but routine for a user to use multiple browsers possible but routine for a user to use multiple browsers
on different computers which will of course have different on different computers that will of course have different
keying material (SACRED <xref target="RFC3760"/> notwithstanding.) keying material (Securely Available Credentials (SACRED) <xref tar
get="RFC3760" format="default"/> notwithstanding).
Thus, users will frequently be alerted to key mismatches which Thus, users will frequently be alerted to key mismatches which
are in fact completely legitimate, with the result that they are in fact completely legitimate, with the result that they
are trained to simply click through them. As it is known that are trained to simply click through them. As it is known that
users routinely will click through far more dire warnings users routinely will click through far more dire warnings
<xref target="cranor-wolf"/>, it seems extremely unlikely that <xref target="cranor-wolf" format="default"/>, it seems extremely unlikely that
any key continuity mechanism will be effective rather than any key continuity mechanism will be effective rather than
simply annoying. simply annoying.
</t> </t>
<t> <t>
Moreover, it is trivial to bypass even this kind of mechanism. Moreover, it is trivial to bypass even this kind of mechanism.
Recall that unlike the case of SSH, the browser never directly Recall that unlike the case of SSH, the browser never directly
gets the peer's identity from the user. Rather, it is provided gets the peer's identity from the user. Rather, it is provided
by the calling service. Even enabling a mechanism of this type by the calling service. Even enabling a mechanism of this type
would require an API to allow the calling service to tell the would require an API to allow the calling service to tell the
browser "this is a call to user X". All the calling service browser "this is a call to user X." All the calling service
needs to do to avoid triggering a key continuity warning needs to do to avoid triggering a key continuity warning
is to tell the browser that "this is a call to user Y" is to tell the browser that "this is a call to user Y"
where Y is confusable with X. where Y is confusable with X.
Even if the user actually checks the other side's name Even if the user actually checks the other side's name
(which all available evidence indicates is unlikely), (which all available evidence indicates is unlikely),
this would require (a) the browser to use the trusted UI this would require (a) the browser to use the trusted UI
to provide the name and (b) the user to not be fooled by to provide the name and (b) the user to not be fooled by
similar appearing names. similar appearing names.
</t> </t>
</section> </section>
<section title="Short Authentication Strings" anchor="sec.sas"> <section anchor="sec.sas" numbered="true" toc="default">
<name>Short Authentication Strings</name>
<t> <t>
ZRTP <xref target="RFC6189"/> uses a "short authentication string" ZRTP <xref target="RFC6189" format="default"/> uses a "Short Authe
(SAS) which is derived ntication String" (SAS) which is derived
from the key agreement protocol. This SAS is designed to be compar from the key agreement protocol.
ed
<!-- [rfced] Section 4.3.2.2: Is the SAS always derived from the key
agreement protocol (in which case "(SAS), which is" would be correct)
or only sometimes derived from the key agreement protocol (in which
case "(SAS) that is" would be correct)?
Original:
ZRTP [RFC6189] uses a "short authentication string" (SAS) which is
derived from the key agreement protocol. -->
This SAS is designed to be compared
by the users (e.g., read aloud over the voice channel or by the users (e.g., read aloud over the voice channel or
transmitted via an out of band channel) and if confirmed by both s ides precludes MITM transmitted via an out-of-band channel) and if confirmed by both s ides precludes MITM
attack. The intention is that the SAS is used once and then key attack. The intention is that the SAS is used once and then key
continuity (though a different mechanism from that discussed continuity (though a different mechanism from that discussed
above) is used thereafter. above) is used thereafter.
<!-- [rfced] Section 4.3.2.2: Should "though a different mechanism"
be "through a different mechanism" or "although using a different
mechanism" here?
Original:
The intention is that the SAS is used
once and then key continuity (though a different mechanism from that
discussed above) is used thereafter. -->
</t> </t>
<t> <t>
Unfortunately, the SAS does not offer a practical solution to the Unfortunately, the SAS does not offer a practical solution to the
problem of a compromised calling service. "Voice conversion " systems, which modify problem of a compromised calling service. "Voice conversion " systems, which modify
voice from one speaker to make it sound like another, voice from one speaker to make it sound like another,
are an active area of research. are an active area of research.
These systems are already good enough to fool both These systems are already good enough to fool both
automatic recognition systems <xref target="farus-conversion"/> an automatic recognition systems <xref target="farrus-conversion" for
d mat="default"/> and
humans <xref target="kain-conversion"/> in many cases, and are of humans <xref target="kain-conversion" format="default"/> in many c
course likely ases, and are of course likely
to improve in future, especially in an environment where the user just wants to improve in future, especially in an environment where the user just wants
to get on with the phone call. to get on with the phone call.
Thus, even if SAS is effective today, it is likely not to be so fo r much longer. Thus, even if the SAS is effective today, it is likely not to be s o for much longer.
</t> </t>
<t> <t>
Additionally, it is unclear that users will actually use an SAS. Additionally, it is unclear that users will actually use an SAS.
As discussed above, the browser UI constraints preclude requiring As discussed above, the browser UI constraints preclude requiring
the SAS exchange prior to completing the call and so it must be the SAS exchange prior to completing the call and so it must be
voluntary; at most the browser will provide some UI indicator that the voluntary; at most the browser will provide some UI indicator that the
SAS has not yet been checked. However, it is well-known that when SAS has not yet been checked. However, it is well known that when
faced with optional security mechanisms, many users simply faced with optional security mechanisms, many users simply
ignore them <xref target="whitten-johnny"/>. ignore them <xref target="whitten-johnny" format="default"/>.
</t> </t>
<t> <t>
Once users have checked the SAS once, key continuity Once users have checked the SAS once, key continuity
is required to avoid them needing to check it on every call. is required to avoid them needing to check it on every call.
However, this is problematic for reasons indicated in However, this is problematic for reasons indicated in
<xref target="sec.key-continuity"/>. <xref target="sec.key-continuity" format="default"/>.
In principle it is of course possible to render a different In principle it is of course possible to render a different
UI element to indicate that calls are using an unauthenticated UI element to indicate that calls are using an unauthenticated
set of keying material (recall that the attacker can just present set of keying material (recall that the attacker can just present
a slightly different name so that the attack shows the a slightly different name so that the attack shows the
same UI as a call to a new device or to someone you haven't same UI as a call to a new device or to someone you haven't
called before) but as a practical matter, users simply ignore called before), but as a practical matter, users simply ignore
such indicators even in the rather more dire case of mixed such indicators even in the rather more dire case of mixed
content warnings. content warnings.
</t> </t>
</section> </section>
<section title="Third Party Identity" anchor="sec.third-party-id"> <section anchor="sec.third-party-id" numbered="true" toc="default">
<name>Third-Party Identity</name>
<t> <t>
The conventional approach to providing communications identity The conventional approach to providing communications identity
has of course been to have some third party identity system has of course been to have some third-party identity system
(e.g., PKI) to authenticate the endpoints. Such mechanisms (e.g., PKI) to authenticate the endpoints. Such mechanisms
have proven to be too cumbersome for use by typical users have proven to be too cumbersome for use by typical users
(and nearly too cumbersome for administrators). (and nearly too cumbersome for administrators).
However, However,
a new generation of Web-based identity providers (BrowserID, Feder ated Google Login, a new generation of Web-based identity providers (BrowserID, Feder ated Google Login,
Facebook Connect, OAuth <xref target="RFC6749"/>, OpenID <xref tar get="OpenID"/>, WebFinger <xref target="RFC7033"/>), has recently been developed Facebook Connect, OAuth <xref target="RFC6749" format="default"/>, OpenID <xref target="OpenID" format="default"/>, WebFinger <xref target="RFC703 3" format="default"/>) has recently been developed
and use Web technologies to provide lightweight (from the user's and use Web technologies to provide lightweight (from the user's
perspective) third-party authenticated transactions. perspective) third-party authenticated transactions.
It is possible to use systems of this type to authenticate WebRTC calls, It is possible to use systems of this type to authenticate WebRTC calls,
linking them to existing user notions of identity linking them to existing user notions of identity
(e.g., Facebook adjacencies). Specifically, the third-party (e.g., Facebook adjacencies). Specifically, the third-party
identity system is used to bind the user's identity to identity system is used to bind the user's identity to
cryptographic keying material which is then used to cryptographic keying material which is then used to
authenticate the calling endpoints. authenticate the calling endpoints.
Calls which are authenticated Calls which are authenticated
in this fashion are naturally resistant even to active MITM attack in this fashion are naturally resistant even to active MITM attack
by the calling site. by the calling site.
</t> </t>
<t> <t>
Note that there is one special case in which PKI-style certificate s Note that there is one special case in which PKI-style certificate s
do provide a practical solution: calls from end-users to do provide a practical solution: calls from end users to
large sites. For instance, if you are making a call large sites. For instance, if you are making a call
to Amazon.com, then Amazon can easily get a certificate to Amazon.com, then Amazon can easily get a certificate
to authenticate their media traffic, just as they get to authenticate their media traffic, just as they get
one to authenticate their Web traffic. This does not provide one to authenticate their Web traffic. This does not provide
additional security value in cases in which the calling site additional security value in cases in which the calling site
and the media peer are one in the same, but might be useful and the media peer are one and the same, but might be useful
in cases in which third parties (e.g., ad networks or in cases in which third parties (e.g., ad networks or
retailers) arrange for calls but do not participate in them. retailers) arrange for calls but do not participate in them.
</t> </t>
</section> </section>
<section anchor="sec.page-access" numbered="true" toc="default">
<section title="Page Access to Media" anchor="sec.page-access"> <name>Page Access to Media</name>
<t> <t>
Identifying the identity of the far media endpoint is a Identifying the identity of the far media endpoint is a
necessary but not sufficient condition for providing media necessary but not sufficient condition for providing media
security. In WebRTC, media flows are rendered into security. In WebRTC, media flows are rendered into
HTML5 MediaStreams which can be manipulated by the calling HTML5 MediaStreams which can be manipulated by the calling
site. Obviously, if the site can modify or view the media, site. Obviously, if the site can modify or view the media,
then the user is not getting the level of assurance they then the user is not getting the level of assurance they
would expect from being able to authenticate their peer. would expect from being able to authenticate their peer.
In many cases, this is acceptable because the user values In many cases, this is acceptable because the user values
site-based special effects over complete security from the site-based special effects over complete security from the
site. However, there are also cases where users wish to site. However, there are also cases where users wish to
know that the site cannot interfere. In order to facilitate know that the site cannot interfere. In order to facilitate
that, it will be necessary to provide features whereby that, it will be necessary to provide features whereby
the site can verifiably give up access to the media streams. the site can verifiably give up access to the media streams.
This verification must be possible both from the local This verification must be possible both from the local
side and the remote side. I.e., users must be able to verify side and the remote side. That is, users must be able to verify
that the person called has engaged a secure media that the person called has engaged a secure media
mode (see <xref target="sec.malicious"/>). In order to achieve thi s it will be necessary to mode (see <xref target="sec.malicious" format="default"/>). In ord er to achieve this, it will be necessary to
cryptographically bind an indication of the local media cryptographically bind an indication of the local media
access policy into the cryptographic authentication access policy into the cryptographic authentication
procedures detailed in the previous sections. procedures detailed in the previous sections.
</t> </t>
<t> <t>
It should be noted that the use of this secure media mode is It should be noted that the use of this secure media mode is
left to the discretion of the site. When such a mode is left to the discretion of the site. When such a mode is
engaged, the browser will need to provide indicia to the user engaged, the browser will need to provide indicia to the user
that the associated media has been authenticated as coming from that the associated media has been authenticated as coming from
the identified user. This allows WebRTC services that wish to the identified user. This allows WebRTC services that wish to
claim end-to-end security to do so in a way that can be easily claim end-to-end security to do so in a way that can be easily
verified by the user. This model requires that the remote verified by the user. This model requires that the remote
party's browser be included in the TCB, as described in party's browser be included in the TCB, as described in
<xref target="sec.web-security"/>. <xref target="sec.web-security" format="default"/>.
</t> </t>
</section> </section>
</section> </section>
<section title="Malicious Peers" anchor="sec.malicious"> <section anchor="sec.malicious" numbered="true" toc="default">
<name>Malicious Peers</name>
<t> <t>
One class of attack that we do not generally try to prevent One class of attack that we do not generally try to prevent
is malicious peers. For instance, no matter what confidentiality is malicious peers. For instance, no matter what confidentiality
measures you employ the person you are talking to might record measures you employ the person you are talking to might record
the call and publish it on the Internet. Similarly, we do the call and publish it on the Internet. Similarly, we do
not attempt to prevent them from using voice or video processing not attempt to prevent them from using voice or video processing
technology from hiding or changing their appearance. technology from hiding or changing their appearance.
While technologies (DRM, etc.) do exist to attempt to address While technologies (Digital Rights Management (DRM), etc.) do exist to attempt to address
these issues, they are generally not compatible with open these issues, they are generally not compatible with open
systems and WebRTC does not address them. systems and WebRTC does not address them.
<!-- [rfced] Section 4.3.3: We found this sentence confusing.
Does "from using voice or video processing technology from hiding
or changing their appearance" mean "from using voice or video
processing technology to hide or change their appearance," or
something else?
Also, for ease of the reader, we expanded "DRM" as "Digital Rights
Management." Please let us know if this is incorrect.
Original:
Similarly, we do not attempt to
prevent them from using voice or video processing technology from
hiding or changing their appearance. While technologies (DRM, etc.)
do exist to attempt to address these issues, they are generally not
compatible with open systems and WebRTC does not address them.
Currently:
... While technologies (Digital
Rights Management (DRM), etc.) do exist to attempt to address these
issues, they are generally not compatible with open systems and
WebRTC does not address them. -->
</t> </t>
<t> <t>
Similarly, we make no attempt to prevent prank calling or Similarly, we make no attempt to prevent prank calling or
other unwanted calls. In general, this is in the scope of the other unwanted calls. In general, this is in the scope of the
calling site, though because WebRTC does offer some forms of calling site, though because WebRTC does offer some forms of
strong authentication, that may be useful as part of a defense strong authentication, that may be useful as part of a defense
against such attacks. against such attacks.
</t> </t>
</section> </section>
</section> </section>
<section title="Privacy Considerations" anchor="sec.privacy"> <section anchor="sec.privacy" numbered="true" toc="default">
<section title="Correlation of Anonymous Calls"> <name>Privacy Considerations</name>
<section numbered="true" toc="default">
<name>Correlation of Anonymous Calls</name>
<t> <t>
While persistent endpoint identifiers can be a useful security While persistent endpoint identifiers can be a useful security
feature (see <xref target="sec.key-continuity"/>) they can feature (see <xref target="sec.key-continuity" format="default"/>), they can
also represent a privacy threat in settings where the user also represent a privacy threat in settings where the user
wishes to be anonymous. WebRTC provides a number of possible wishes to be anonymous. WebRTC provides a number of possible
persistent identifiers such as DTLS certificates persistent identifiers such as DTLS certificates
(if they are reused between connections) and RTCP CNAMES (if they are reused between connections) and RTCP CNAMEs
(if generated according to <xref target="RFC6222"/> rather (if generated according to <xref target="RFC6222" format="default"/>
than the privacy preserving mode of <xref target="RFC7022"/>). rather
than the privacy-preserving mode of <xref target="RFC7022" format="d
efault"/>).
In order to prevent this type of correlation, browsers need to In order to prevent this type of correlation, browsers need to
provide mechanisms to reset these identifiers (e.g., with the provide mechanisms to reset these identifiers (e.g., with the
same lifetime as cookies). Moreover, the API should provide same lifetime as cookies). Moreover, the API should provide
mechanisms to allow sites intended for anonymous calling mechanisms to allow sites intended for anonymous calling
to force the minting of fresh identifiers. In addition, to force the minting of fresh identifiers. In addition,
IP addresses can be a source of call linkage IP addresses can be a source of call linkage
<xref target="I-D.ietf-rtcweb-ip-handling"/>. <xref target="RFC8828" format="default"/>.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Browser Fingerprinting"> <name>Browser Fingerprinting</name>
<t> <t>
Any new set of API features adds a risk of browser fingerprinting, Any new set of API features adds a risk of browser fingerprinting,
and WebRTC is no exception. Specifically, sites can use the and WebRTC is no exception. Specifically, sites can use the
presence or absence of specific devices as a browser fingerprint. presence or absence of specific devices as a browser fingerprint.
In general, the API needs to be balanced between functionality In general, the API needs to be balanced between functionality
and the incremental fingerprint risk. See <xref target="Fingerprint ing"/>. and the incremental fingerprint risk. See <xref target="Fingerprint ing" format="default"/>.
</t> </t>
</section> </section>
</section> </section>
</section> </section>
<section anchor="sec.sec_cons" numbered="true" toc="default">
<section title="Security Considerations" anchor="sec.sec_cons"> <name>Security Considerations</name>
<t>This entire document is about security.</t> <t>This entire document is about security.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Acknowledgements"> <name>IANA Considerations</name>
<t> <t>This document has no IANA actions.</t>
Bernard Aboba, Harald Alvestrand, Dan Druta,
Cullen Jennings, Alan Johnston, Hadriel Kaplan (S 4.2.1), Matthew Ka
ufman,
Martin Thomson, Magnus Westerlund.
</t>
<t></t>
</section>
<section title="IANA Considerations">
<t>There are no IANA considerations.</t>
</section>
<section title="Changes Since -04">
<t>
<list style="symbols">
<t>Replaced RTCWEB and RTC-Web with WebRTC, except when referring to t
he IETF WG</t>
<t>Removed discussion of the IFRAMEd advertisement case, since we deci
ded not to
treat it specially.</t>
<t>Added a privacy section considerations section.</t>
<t>Significant edits to the SAS section to reflect Alan Johnston's com
ments.</t>
<t>Added some discussion if IP location privacy and Tor.</t>
<t>Updated the "communications consent" section to reflrect draft-ietf
.</t>
<t>Added a section about "malicious peers".</t>
<t>Added a section describing screen sharing threats.</t>
<t>Assorted editorial changes.</t>
</list>
</t>
</section> </section>
</middle> </middle>
<back> <back>
<references>
<name>References</name>
<references>
<name>Normative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.
xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3261.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3552.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3711.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2818.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5479.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5763.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6347.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4568.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4251.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3760.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6189.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8445.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6222.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6454.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6455.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6749.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7022.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7033.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7675.
xml"/>
<references title="Normative References"> <!--draft-ietf-rtcweb-security-arch: 8827 -->
&RFC2119; <reference anchor="RFC8827" target="https://www.rfc-editor.org/info/rfc8827">
&RFC8174; <front>
</references> <title>WebRTC Security Architecture</title>
<references title="Informative References"> <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
&RFC3261; <organization/>
&RFC3552; </author>
&RFC3711; <date month='June' year='2020'/>
&RFC2818; </front>
&RFC5479; <seriesInfo name="RFC" value="8827"/>
&RFC5763; <seriesInfo name="DOI" value="10.17487/RFC8827"/>
&RFC6347; </reference>
&RFC4568;
&RFC4251;
&RFC3760;
&RFC6189;
&RFC8445;
&RFC6222;
&RFC6454;
&RFC6455;
&RFC6749;
&RFC7022;
&RFC7033;
&RFC7675;
&I-D.ietf-rtcweb-security-arch;
&I-D.ietf-rtcweb-ip-handling;
&I-D.ietf-rtcweb-overview;
<reference anchor="abarth-rtcweb">
<front>
<title>Prompting the user is security failure</title>
<author initials="A." surname="Barth">
<organization></organization>
</author>
<!-- Date from PDF properties -->
<date day="19" month="September" year="2010" />
</front>
<seriesInfo name="" value="RTC-Web Workshop"/>
<format target="http://rtc-web.alvestrand.com/home/papers/barth-security
-prompt.pdf?attredirects=0" type="PDF"/>
</reference>
<reference anchor="whitten-johnny">
<front>
<title>Why Johnny Can't Encrypt: A Usability Evaluation of PGP 5.0</ti
tle>
<author initials="A." surname="Whitten">
<organization></organization>
</author>
<author initials="J.D." surname="Tygar">
<organization></organization>
</author>
<!-- Date of USENIX Security Symposium -->
<date month="August" year="1999" />
</front>
<seriesInfo name="" value="Proceedings of the 8th USENIX Security Sympos
ium, 1999"/>
</reference>
<reference anchor="cranor-wolf">
<front>
<title>Crying Wolf: An Empirical Study of SSL Warning Effectiveness</t
itle>
<author initials="J." surname="Sunshine">
<organization></organization>
</author>
<author initials="S." surname="Egelman"> <!-- draft-ietf-rtcweb-ip-handling: 8828 -->
<organization></organization> <reference anchor="RFC8828" target="https://www.rfc-editor.org/info/rfc8828">
</author> <front>
<author initials="H." surname="Almuhimedi"> <title>WebRTC IP Address Handling Requirements</title>
<organization></organization> <author initials="J" surname="Uberti" fullname="Justin Uberti">
</author> <organization />
<author initials="N." surname="Atri"> </author>
<organization></organization>
</author>
<author initials="L." surname="cranor">
<organization></organization>
</author>
<!-- Date of USENIX Security Symposium --> <date month="June" year="2020" />
<date month="August" year="2009" /> </front>
</front> <seriesInfo name="RFC" value="8828" />
<seriesInfo name="DOI" value="10.17487/RFC8828"/>
</reference>
<seriesInfo name="" value="Proceedings of the 18th USENIX Security Sympo <!-- draft-ietf-rtcweb-overview: RFC 8825 -->
sium, 2009"/> <reference anchor="RFC8825" target="https://www.rfc-editor.org/info/rfc8825">
<front>
<title>Overview: Real-Time Protocols for Browser-Based Applications</title>
<author initials="H." surname="Alvestrand" fullname="Harald T. Alvestrand">
<organization />
</author>
<date month="June" year="2020" />
</front>
<seriesInfo name="RFC" value="8825" />
<seriesInfo name="DOI" value="10.17487/RFC8825"/>
</reference>
</reference> <reference anchor="abarth-rtcweb" target="http://rtc-web.alvestrand.com/
home/papers/barth-security-prompt.pdf?attredirects=0">
<front>
<title>Prompting the user is security failure</title>
<author initials="A." surname="Barth">
<organization/>
</author>
<date month="September" year="2010"/>
</front>
<refcontent>RTC-Web Workshop</refcontent>
</reference>
<reference anchor="kain-conversion"> <!-- [rfced] Informative References:
<front> The URL provided for [abarth-rtcweb] in the original XML file -
<title>Design and Evaluation of a Voice Conversion Algorithm based on <http://rtc-web.alvestrand.com/home/papers/
Spectral Envelope Mapping and Residual Prediction</title> barth-security-prompt.pdf?attredirects=0> - steers to
<https://672ad43e-a-6ea19bdf-s-sites.googlegroups.com/
a/alvestrand.com/rtc-web/home/papers/
barth-security-prompt.pdf?attachauth= ...(a very long string that is
different each time)...&attredirects=0>.
<author initials="A." surname="Kain"> Is
<organization></organization> <http://rtc-web.alvestrand.com/home/papers/barth-security-prompt.pdf?attredirect
</author> s=0>
considered the most stable URL available? Or, should the URL not be included
at all?
<author initials="M." surname="Macon"> Original:
<organization></organization> <format
</author> target="http://rtc-web.alvestrand.com/home/papers/barth-security-prom
pt.pdf?attredirects=0\
" type="PDF"/>
-->
<!-- Date of ICASSP 2001 --> <reference anchor="whitten-johnny" target="https://www.usenix.org/legacy
<date month="May" year="2001" /> /publications/library/proceedings/sec99/whitten.html">
</front> <front>
<title>Why Johnny Can't Encrypt: A Usability Evaluation of PGP 5.0</
title>
<author initials="A." surname="Whitten">
<organization/>
</author>
<author initials="J.D." surname="Tygar">
<organization/>
</author>
<date month="August" year="1999"/>
</front>
<refcontent>Proceedings of the 8th USENIX Security Symposium</refcontent
>
</reference>
<seriesInfo name="" value="Proceedings of ICASSP, May 2001"/> <reference anchor="cranor-wolf" target="https://www.usenix.org/legacy/ev
</reference> ent/sec09/tech/full_papers/sunshine.pdf">
<front>
<title>Crying Wolf: An Empirical Study of SSL Warning Effectiveness<
/title>
<author initials="J." surname="Sunshine">
<organization/>
</author>
<author initials="S." surname="Egelman">
<organization/>
</author>
<author initials="H." surname="Almuhimedi">
<organization/>
</author>
<author initials="N." surname="Atri">
<organization/>
</author>
<author initials="L." surname="Cranor">
<organization/>
</author>
<date month="August" year="2009"/>
</front>
<refcontent>Proceedings of the 18th USENIX Security Symposium</refconten
t>
</reference>
<reference anchor="farus-conversion"> <reference anchor="kain-conversion">
<front> <front>
<title>Speaker Recognition Robustness to Voice Conversion</title> <title>Design and Evaluation of a Voice Conversion Algorithm based
on Spectral Envelope Mapping and Residual Prediction</title>
<author initials="A." surname="Kain">
<organization/>
</author>
<author initials="M." surname="Macon">
<organization/>
</author>
<date month="May" year="2001"/>
</front>
<seriesInfo name="DOI" value="10.1109/ICASSP.2001.941039"/>
<refcontent>Proceedings of the 2001 IEEE International Conference on
Acoustics, Speech, and Signal Processing (ICASSP)</refcontent>
</reference>
<author initials="M." surname="Farrus"> <reference anchor="farrus-conversion">
<organization></organization> <front>
</author> <title>Speaker Recognition Robustness to Voice Conversion</title>
<author initials="D." surname="Erro"> <author initials="M." surname="Farrus">
<organization></organization> <organization/>
</author> </author>
<author initials="J." surname="Hernando"> <author initials="D." surname="Erro">
<organization></organization> <organization/>
</author> </author>
<author initials="J." surname="Hernando">
<organization/>
</author>
<date month="January" year="2008"/>
</front>
</reference>
<!-- Date from http://www.researchgate.net/publication/228819912 --> <reference anchor="huang-w2sp">
<date month="January" year="2008" /> <front>
</front> <title>Talking to Yourself for Fun and Profit</title>
</reference> <author initials="L-S." surname="Huang">
<organization/>
</author>
<author initials="E.Y." surname="Chen">
<organization/>
</author>
<author initials="A." surname="Barth">
<organization/>
</author>
<author initials="E." surname="Rescorla">
<organization/>
</author>
<author initials="C." surname="Jackson">
<organization/>
</author>
<date month="May" year="2011"/>
</front>
<refcontent>Web 2.0 Security and Privacy (W2SP 2011)</refcontent>
</reference>
<reference anchor="huang-w2sp"> <reference anchor="finer-grained">
<front> <front>
<title>Talking to Yourself for Fun and Profit</title> <title>Beware of Finer-Grained Origins</title>
<author initials="C." surname="Jackson">
<organization/>
</author>
<author initials="A." surname="Barth">
<organization/>
</author>
<date month="July" year="2008"/>
</front>
<refcontent>Web 2.0 Security and Privacy (W2SP 2008)</refcontent>
</reference>
<author initials="L-S." surname="Huang"> <!-- [rfced] Is the [CORS] reference still correct? Should this document
<organization></organization> instead refer to <https://fetch.spec.whatwg.org/>? Perhaps
</author> <https://fetch.spec.whatwg.org/#http-cors-protocol>, more specifically?
<author initials="E.Y." surname="Chen">
<organization></organization>
</author>
<author initials="A." surname="Barth">
<organization></organization>
</author>
<author initials="E." surname="Rescorla">
<organization></organization>
</author>
<author initials="C." surname="Jackson">
<organization></organization>
</author>
<!-- Date from PDF properties --> Original:
<date month="May" year="2011" /> [CORS] van Kesteren, A., "Cross-Origin Resource Sharing", January
</front> 2014.
<seriesInfo name="" value="W2SP, 2011"/> When we search for this document, we find this link
</reference> <https://www.w3.org/TR/2009/WD-cors-20090317/>, which gives the following
warning:
<reference anchor="finer-grained"> This version is outdated!
<front> For the latest version, please look at https://www.w3.org/TR/cors/.
<title>Beware of Finer-Grained Origins</title>
<author initials="A." surname="Barth"> <https://www.w3.org/TR/cors/> redirects to <https://fetch.spec.whatwg.org/>.
<organization></organization>
</author>
<author initials="C." surname="Jackson">
<organization></organization>
</author>
<!-- Date from PDF properties --> On <https://fetch.spec.whatwg.org/>, the reference for [CORS] refers back to
<date month="July" year="2008" /> <https://www.w3.org/TR/cors/>:
</front>
<seriesInfo name="" value="W2SP, 2008"/> [CORS]
</reference> Anne van Kesteren. Cross-Origin Resource Sharing. 2 June 2020. REC. URL:
https://www.w3.org/TR/cors/
<reference anchor="CORS"> <https://www.w3.org/TR/2020/SPSD-cors-20200602/> says that new implementations
<front> should follow the "Fetch API Living Standard".
<title>Cross-Origin Resource Sharing</title>
<author initials="A." surname="van Kesteren"> Please review and let us know if any updates are needed.
<organization></organization> -->
</author>
<!-- Date from http://www.w3.org/TR/2014/REC-cors-20140116/ --> <reference anchor="CORS">
<date day="16" month="January" year="2014" /> <front>
</front> <title>Cross-Origin Resource Sharing</title>
<format target="http://www.w3.org/TR/cors/" type="TXT"/> <author initials="A." surname="van Kesteren">
</reference> <organization/>
</author>
<date month="January" year="2014"/>
</front>
</reference>
<reference anchor="SWF"> <reference anchor="SWF" target="http://www.adobe.com/content/dam/Adobe/e
<front> n/devnet/swf/pdf/swf_file_format_spec_v10.pdf">
<title>SWF File Format Specification Version 19</title> <front>
<title>SWF File Format Specification Version 19</title>
<author/>
<date month="April" year="2013"/>
</front>
</reference>
<author surname="Adobe"> <!-- [rfced] Informative References:
<organization></organization> The URL provided for [SWF] in the original XML file -
</author> <http://www.adobe.com/content/dam/Adobe/en/devnet/swf/pdf/
swf_file_format_spec_v10.pdf> - steers to
<https://www.adobe.com/content/dam/acom/en/devnet/swf/pdf/
swf_file_format_spec_v10.pdf>, which in turn yields a 404.
Please provide a working and stable URL.
<!-- Date from PDF properties --> Original:
<date day="23" month="April" year="2013" /> [SWF] "SWF File Format Specification Version 19", April 2013. -->
</front>
<format target="http://www.adobe.com/content/dam/Adobe/en/devnet/swf/pdf
/swf_file_format_spec_v10.pdf" type="PDF"/>
</reference>
<reference anchor="XmlHttpRequest"> <reference anchor="XmlHttpRequest" target="https://www.w3.org/TR/XMLHttp Request/">
<front> <front>
<title>XMLHttpRequesti Level 2</title> <title>XMLHttpRequest Level 2</title>
<author initials="A." surname="van Kesteren"> <author initials="A." surname="van Kesteren">
<organization></organization> <organization/>
</author> </author>
<date day="17" month="January" year="2012"/> <date month="January" year="2012"/>
</front> </front>
<format target="http://www.w3.org/TR/XMLHttpRequest/" type="TXT"/> </reference>
</reference>
<reference anchor="Fingerprinting"> <!-- [rfced] Informative References: The URL as provided for
<front> [XmlHttpRequest] in the original document -
<title>Fingerprinting Guidance for Web Specification Authors (Draft)< <http://www.w3.org/TR/XMLHttpRequest/> - steers to a page with the
/title> title "XMLHttpRequest Level 1," dated October 2016. When we did a
Google search for "XMLHttpRequest Level 2," we found
<https://www.w3.org/TR/2012/WD-XMLHttpRequest-20120117/>, which is
partially obscured by a red box that says "This version is
outdated!" The link in the box in turn steers to the October 2016
"XMLHttpRequest Level 1" page.
<author surname="W3C"> Please advise.
<organization></organization>
</author>
<date day="24" month="November" year="2013" /> Original:
</front> [XmlHttpRequest]
<format target="https://www.w3.org/TR/fingerprinting-guidance/#acknowle van Kesteren, A., "XMLHttpRequest Level 2", January 2012. -->
dgement/" type="TXT"/>
</reference>
<reference anchor="OpenID"> <reference anchor="Fingerprinting" target="https://www.w3.org/TR/fingerp rinting-guidance/#acknowledgement/">
<front> <front>
<title>OpenID Connect Core 1.0</title> <title>Fingerprinting Guidance for Web Specification Authors (Draft)
</title>
<author/>
<date month="November" year="2013"/>
</front>
</reference>
<!-- [rfced] Informative References: The URL provided for
[Fingerprinting] in the original XML file -
<https://www.w3.org/TR/fingerprinting-guidance/#acknowledgement/> -
steers to a document with the title "Mitigating Browser
Fingerprinting in Web Specifications." Should the reference be updated? If
not, please provide the correct URL for the document listed below - perhaps
<https://www.w3.org/standards/history/fingerprinting-guidance> or
<https://www.w3.org/TR/fingerprinting-guidance/>?
Original:
[Fingerprinting]
"Fingerprinting Guidance for Web Specification Authors
(Draft)", November 2013. -->
<reference anchor="OpenID" target="https://openid.net/specs/openid-conne
ct-core-1_0.html">
<front>
<title>OpenID Connect Core 1.0</title>
<author initials="N." surname="Sakimura"> <author initials="N." surname="Sakimura">
<organization></organization> <organization/>
</author> </author>
<author initials="J." surname="Bradley"> <author initials="J." surname="Bradley">
<organization></organization> <organization/>
</author> </author>
<author initials="M." surname="Jones"> <author initials="M." surname="Jones">
<organization></organization> <organization/>
</author> </author>
<author initials="B." surname="de Medeiros"> <author initials="B." surname="de Medeiros">
<organization></organization> <organization/>
</author> </author>
<author initials="C." surname="Mortimore"> <author initials="C." surname="Mortimore">
<organization></organization> <organization/>
</author> </author>
<date month="November" year="2014"/>
<date day="8" month="November" year="2014" />
</front> </front>
<format target="https://openid.net/specs/openid-connect-core-1_0.html/ </reference>
" type="HTML"/> </references>
</reference>
</references> </references>
<section numbered="false" toc="default">
<name>Acknowledgements</name>
<t>
<contact fullname="Bernard Aboba"/>, <contact fullname="Harald
Alvestrand"/>, <contact fullname="Dan Druta"/>,
<contact fullname="Cullen Jennings"/>, <contact fullname="Alan
Johnston"/>, <contact fullname="Hadriel Kaplan"/> (<xref
target="sec.ice"/>), <contact fullname="Matthew Kaufman"/>,
<contact fullname="Martin Thomson"/>, <contact fullname="Magnus West
erlund"/>.
</t>
</section>
</back>
<!-- [rfced] Please let us know how/if the following should be made
consistent:
iframe / IFRAME (also per draft-ietf-rtcweb-security-arch)
calling-service.example.com/ vs. calling-service.example.com
(We also see "http://anything.example.org/".)
CROSS-PROTOCOL attacks (Section 3.3) /
cross-protocol attacks (Section 4.2) Is the capitalization
supposed to indicate emphasis? -->
</back>
</rfc> </rfc>
 End of changes. 221 change blocks. 
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