draft-ietf-oauth-security-topics-05.txt   draft-ietf-oauth-security-topics-06.txt 
Open Authentication Protocol T. Lodderstedt, Ed. Open Authentication Protocol T. Lodderstedt, Ed.
Internet-Draft YES.com AG Internet-Draft YES.com AG
Intended status: Best Current Practice J. Bradley Intended status: Best Current Practice J. Bradley
Expires: September 19, 2018 Yubico Expires: November 21, 2018 Yubico
A. Labunets A. Labunets
Facebook Facebook
March 18, 2018 D. Fett
University of Stuttgart
May 20, 2018
OAuth 2.0 Security Best Current Practice OAuth 2.0 Security Best Current Practice
draft-ietf-oauth-security-topics-05 draft-ietf-oauth-security-topics-06
Abstract Abstract
This document describes best current security practices for OAuth This document describes best current security practices for OAuth
2.0.. It updates and extends the OAuth 2.0 Security Threat Model to 2.0. It updates and extends the OAuth 2.0 Security Threat Model to
incorporate practical experiences gathered since OAuth 2.0 was incorporate practical experiences gathered since OAuth 2.0 was
published and cover new threats relevant due to the broader published and covers new threats relevant due to the broader
application of OAuth 2.0. application of OAuth 2.0.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 19, 2018. This Internet-Draft will expire on November 21, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4 2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Protecting redirect-based flows . . . . . . . . . . . . . 4 2.1. Protecting redirect-based flows . . . . . . . . . . . . . 4
2.2. Token Replay Prevention . . . . . . . . . . . . . . . . . 5 2.2. Token Replay Prevention . . . . . . . . . . . . . . . . . 5
3. Attacks and Mitigations . . . . . . . . . . . . . . . . . . . 5 3. Attacks and Mitigations . . . . . . . . . . . . . . . . . . . 5
3.1. Insufficient redirect URI validation . . . . . . . . . . 5 3.1. Insufficient redirect URI validation . . . . . . . . . . 5
3.1.1. Attacks on Authorization Code Grant . . . . . . . . . 5 3.1.1. Attacks on Authorization Code Grant . . . . . . . . . 6
3.1.2. Attacks on Implicit Grant . . . . . . . . . . . . . . 6 3.1.2. Attacks on Implicit Grant . . . . . . . . . . . . . . 7
3.1.3. Proposed Countermeasures . . . . . . . . . . . . . . 8 3.1.3. Proposed Countermeasures . . . . . . . . . . . . . . 8
3.2. Authorization code leakage via referrer headers . . . . . 9 3.2. Code or State Leakage from Client or AS via Referrer
Headers . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2.1. Proposed Countermeasures . . . . . . . . . . . . . . 9 3.2.1. Proposed Countermeasures . . . . . . . . . . . . . . 9
3.3. Attacks in the Browser . . . . . . . . . . . . . . . . . 10 3.3. Attacks through the Browser History . . . . . . . . . . . 10
3.3.1. Code in browser history . . . . . . . . . . . . . . . 10 3.3.1. Code in Browser History . . . . . . . . . . . . . . . 10
3.3.2. Access token in browser history . . . . . . . . . . . 10 3.3.2. Access Token in Browser History . . . . . . . . . . . 10
3.4. Mix-Up . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.4. Mix-Up . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5. Code Injection . . . . . . . . . . . . . . . . . . . . . 11 3.4.1. Attack Description . . . . . . . . . . . . . . . . . 11
3.5.1. Proposed Countermeasures . . . . . . . . . . . . . . 13 3.4.2. Countermeasures . . . . . . . . . . . . . . . . . . . 13
3.6. Cross Site Request Forgery . . . . . . . . . . . . . . . 15 3.5. Code Injection . . . . . . . . . . . . . . . . . . . . . 14
3.7. Access Token Leakage at the Resource Server . . . . . . . 15 3.5.1. Proposed Countermeasures . . . . . . . . . . . . . . 16
3.7.1. Access Token Phishing by Counterfeit Resource Server 15 3.6. Cross Site Request Forgery . . . . . . . . . . . . . . . 17
3.7.1.1. Metadata . . . . . . . . . . . . . . . . . . . . 16 3.6.1. Proposed Countermeasures . . . . . . . . . . . . . . 17
3.7.1.2. Sender Constrained Access Tokens . . . . . . . . 17 3.7. Access Token Leakage at the Resource Server . . . . . . . 18
3.7.1.3. Audience Restricted Access Tokens . . . . . . . . 19 3.7.1. Access Token Phishing by Counterfeit Resource Server 18
3.7.2. Compromised Resource Server . . . . . . . . . . . . . 20 3.7.1.1. Metadata . . . . . . . . . . . . . . . . . . . . 18
3.8. Open Redirection . . . . . . . . . . . . . . . . . . . . 21 3.7.1.2. Sender Constrained Access Tokens . . . . . . . . 19
3.8.1. Authorization Server as Open Redirector . . . . . . . 21 3.7.1.3. Audience Restricted Access Tokens . . . . . . . . 22
3.8.2. Clients as Open Redirector . . . . . . . . . . . . . 21 3.7.2. Compromised Resource Server . . . . . . . . . . . . . 23
3.9. TLS Terminating Reverse Proxies . . . . . . . . . . . . . 22 3.8. Open Redirection . . . . . . . . . . . . . . . . . . . . 24
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 3.8.1. Authorization Server as Open Redirector . . . . . . . 24
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 3.8.2. Clients as Open Redirector . . . . . . . . . . . . . 24
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23 3.9. TLS Terminating Reverse Proxies . . . . . . . . . . . . . 25
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
7.1. Normative References . . . . . . . . . . . . . . . . . . 23 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
7.2. Informative References . . . . . . . . . . . . . . . . . 24 6. Security Considerations . . . . . . . . . . . . . . . . . . . 26
Appendix A. Document History . . . . . . . . . . . . . . . . . . 26 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 7.1. Normative References . . . . . . . . . . . . . . . . . . 26
7.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Document History . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction 1. Introduction
It's been a while since OAuth has been published in RFC 6749 It's been a while since OAuth has been published in RFC 6749
[RFC6749] and RFC 6750 [RFC6750]. Since publication, OAuth 2.0 has [RFC6749] and RFC 6750 [RFC6750]. Since publication, OAuth 2.0 has
gotten massive traction in the market and became the standard for API gotten massive traction in the market and became the standard for API
protection and, as foundation of OpenID Connect [OpenID], identity protection and, as foundation of OpenID Connect [OpenID], identity
providing. While OAuth was used in a variety of scenarios and providing. While OAuth was used in a variety of scenarios and
different kinds of deployments, the following challenges could be different kinds of deployments, the following challenges could be
observed: observed:
o OAuth implementations are being attacked through known o OAuth implementations are being attacked through known
implementation weaknesses and anti-patterns (XSRF, referrer implementation weaknesses and anti-patterns (XSRF, referrer
header). Although most of these threats are discussed in the header). Although most of these threats are discussed in the
OAuth 2.0 Threat Model and Security Considerations [RFC6819], OAuth 2.0 Threat Model and Security Considerations [RFC6819],
continued exploitation demonstrates there may be a need for more continued exploitation demonstrates there may be a need for more
specific recommendations or that the existing mitigations are too specific recommendations or that the existing mitigations are too
difficult to deploy. difficult to deploy.
o Technology has changed, e.g. the way browsers treat fragments in o Technology has changed, e.g., the way browsers treat fragments in
some situations, which may change the implicit grant's underlying some situations, which may change the implicit grant's underlying
security model. security model.
o OAuth is used in much more dynamic setups than originally o OAuth is used in much more dynamic setups than originally
anticipated, creating new challenges with respect to security. anticipated, creating new challenges with respect to security.
Those challenges go beyond the original scope of RFC 6749 Those challenges go beyond the original scope of RFC 6749
[RFC6749], RFC 6750 [RFC6749], and RFC 6819 [RFC6819]. [RFC6749], RFC 6750 [RFC6749], and RFC 6819 [RFC6819].
OAuth initially assumed a static relationship between client, OAuth initially assumed a static relationship between client,
authorization server and resource servers. The URLs of AS and RS authorization server and resource servers. The URLs of AS and RS
were known to the client at deployment time and built an anchor for were known to the client at deployment time and built an anchor for
the trust relationsship among those parties. The validation whether the trust relationship among those parties. The validation whether
the client talks to a legitimate server was based on TLS server the client talks to a legitimate server was based on TLS server
authentication (see [RFC6819], Section 4.5.4). With the increasing authentication (see [RFC6819], Section 4.5.4). With the increasing
adoption of OAuth, this simple model dissolved and, in several adoption of OAuth, this simple model dissolved and, in several
scenarios, was replaced by a dynamic establishment of the scenarios, was replaced by a dynamic establishment of the
relationship between clients on one side and the authorization and relationship between clients on one side and the authorization and
resource servers of a particular deployment on the other side. This resource servers of a particular deployment on the other side. This
way the same client could be used to access services of different way the same client could be used to access services of different
providers (in case of standard APIs, such as e-Mail or OpenID providers (in case of standard APIs, such as e-Mail or OpenID
Connect) or serves as a frontend to a particular tenant in a multi- Connect) or serves as a frontend to a particular tenant in a multi-
tenancy. Extensions of OAuth, such as [RFC7591] and tenancy. Extensions of OAuth, such as [RFC7591] and
[I-D.ietf-oauth-discovery] were developed in order to support the [I-D.ietf-oauth-discovery] were developed in order to support the
usage of OAuth in dynamic scenarios. As a challenge to the usage of OAuth in dynamic scenarios. As a challenge to the
community, such usage scenarios open up new attack angles, which are community, such usage scenarios open up new attack angles, which are
discussed in this document. discussed in this document.
The remainder of the document is organized as follows: The next The remainder of the document is organized as follows: The next
section summarizes the most important recommendations of the OAuth section summarizes the most important recommendations of the OAuth
working group for every OAuth implementor. Afterwards, a detailed working group for every OAuth implementor. Afterwards, a detailed
analyses of the threats and implementation issues, which can be found analysis of the threats and implementation issues which can be found
in the wild today, is given along with a discussion of potential in the wild today is given along with a discussion of potential
counter measures. countermeasures.
2. Recommendations 2. Recommendations
This section describes the set of security mechanisms the authors This section describes the set of security mechanisms the OAuth
believe should be taken into consideration by the OAuth working group working group recommendeds to OAuth implementers.
to be recommended to OAuth implementers.
2.1. Protecting redirect-based flows 2.1. Protecting redirect-based flows
Authorization servers shall utilize exact matching of client redirect Authorization servers shall utilize exact matching of client redirect
URIs against pre-registered URIs. This measure contributes to the URIs against pre-registered URIs. This measure contributes to the
prevention of leakage of authorization codes and access tokens prevention of leakage of authorization codes and access tokens
(depending on the grant type). It also helps to detect mix up (depending on the grant type). It also helps to detect mix-up
attacks. attacks.
Clients shall avoid any redirects or forwards, which can be Clients shall avoid any redirects or forwards which can be
parameterized by URI query parameters, in order to provide a further parameterized by URI query parameters, in order to provide a further
layer of defence against token leakage. If there is a need for this layer of defence against token leakage. If there is a need for this
kind of redirects, clients are advised to implement appropriate kind of redirects, clients are advised to implement appropriate
counter measures against open redirection, e.g. as described by the countermeasures against open redirection, e.g., as described by the
OWASP [owasp]. OWASP [owasp].
Clients shall ensure to only process redirect responses of the OAuth Clients shall ensure to only process redirect responses of the OAuth
authorization server they send the respective request to and in the authorization server they send the respective request to and in the
same user agent this request was initiated in. In particular, same user agent this request was initiated in. In particular,
clients shall implement appropriate XSRF prevention by utilizing one- clients shall implement appropriate XSRF prevention by utilizing one-
time use XSRF tokens carried in the STATE parameter, which are time use XSRF tokens carried in the "state" parameter, which are
securely bound to the user agent. Moreover, the client shall securely bound to the user agent. Moreover, the client shall
memorize which authorization server it sent an authorization request memorize which authorization server it sent an authorization request
to and bind this information to the user agent and ensure any sub- to and bind this information to the user agent and ensure any sub-
sequent messages are sent to the same authorization server. sequent messages are sent to the same authorization server.
Furthermore, clients should use AS-specific redirect URIs as a means Furthermore, clients should use AS-specific redirect URIs as a means
to identify the AS a particular response came from. Matching this to identify the AS a particular response came from. Matching this
with the before mentioned information regarding the AS the client with the before mentioned information regarding the AS the client
sent the request to helps to detect mix-up attacks. sent the request to helps to detect mix-up attacks.
Note: [I-D.bradley-oauth-jwt-encoded-state] gives advice on how to Note: [I-D.bradley-oauth-jwt-encoded-state] gives advice on how to
implement XSRF prevention and AS matching using signed JWTs in the implement XSRF prevention and AS matching using signed JWTs in the
STATE parameter. "state" parameter.
Clients shall use PKCE [RFC7636] in order to (with the help of the Clients shall use PKCE [RFC7636] in order to (with the help of the
authorization server) detect and prevent attempts to inject (replay) authorization server) detect and prevent attempts to inject (replay)
authorization codes into the authorization response. The PKCE authorization codes into the authorization response. The PKCE
challenges must be transaction-specific and securely bound to the challenges must be transaction-specific and securely bound to the
user agent, in which the transaction was started. OpenID Connect user agent, in which the transaction was started. OpenID Connect
clients may use the "nonce" parameter of the OpenID Connect clients may use the "nonce" parameter of the OpenID Connect
authentication request as specified in [OpenID] in conjunction with authentication request as specified in [OpenID] in conjunction with
the corresponding ID Token claim of the for the same purpose. the corresponding ID Token claim for the same purpose.
Note: although PKCE so far was recommended as mechanism to protect Note: although PKCE so far was recommended as mechanism to protect
native apps, this advice applies to all kinds of OAuth clients, native apps, this advice applies to all kinds of OAuth clients,
including web applications. including web applications.
Authorization servers shall consider the recommendations given in Authorization servers shall consider the recommendations given in
[RFC6819], section 4.4.1.1, on authorization code replay prevention. [RFC6819], Section 4.4.1.1, on authorization code replay prevention.
2.2. Token Replay Prevention 2.2. Token Replay Prevention
Authorization servers shall use TLS-based methods for sender Authorization servers shall use TLS-based methods for sender
constraint access tokens as described in section Section 3.7.1.2, constrained access tokens as described in Section 3.7.1.2, such as
such as token binding [I-D.ietf-oauth-token-binding] or Mutual TLS token binding [I-D.ietf-oauth-token-binding] or Mutual TLS for OAuth
for OAuth 2.0 [I-D.ietf-oauth-mtls]. It is also recommend to use 2.0 [I-D.ietf-oauth-mtls] in order to prevent token replay. It is
end-to-end TLS whenever possible. also recommend to use end-to-end TLS whenever possible.
3. Attacks and Mitigations 3. Attacks and Mitigations
This section gives a detailed description of attacks on OAuth
implementations, along with potential countermeasures. This section
complements and enhances the description given in [RFC6819].
3.1. Insufficient redirect URI validation 3.1. Insufficient redirect URI validation
Some authorization servers allow clients to register redirect URI Some authorization servers allow clients to register redirect URI
patterns instead of complete redirect URIs. In those cases, the patterns instead of complete redirect URIs. In those cases, the
authorization server, at runtime, matches the actual redirect URI authorization server, at runtime, matches the actual redirect URI
parameter value at the authorization endpoint against this pattern. parameter value at the authorization endpoint against this pattern.
This approach allows clients to encode transaction state into This approach allows clients to encode transaction state into
additional redirect URI parameters or to register just a single additional redirect URI parameters or to register just a single
pattern for multiple redirect URIs. As a downside, it turned out to pattern for multiple redirect URIs. As a downside, it turned out to
be more complex to implement and error prone to manage than exact be more complex to implement and error prone to manage than exact
skipping to change at page 5, line 51 skipping to change at page 6, line 10
o by exposing the OAuth credentials to an attacker by utilizing an o by exposing the OAuth credentials to an attacker by utilizing an
open redirector at the client in conjunction with the way user open redirector at the client in conjunction with the way user
agents handle URL fragments. agents handle URL fragments.
3.1.1. Attacks on Authorization Code Grant 3.1.1. Attacks on Authorization Code Grant
For a public client using the grant type code, an attack would look For a public client using the grant type code, an attack would look
as follows: as follows:
Let's assume the redirect URL pattern "https://*.example.com/*" had Let's assume the redirect URL pattern "https://*.somesite.example/*"
been registered for the client "s6BhdRkqt3". This pattern allows had been registered for the client "s6BhdRkqt3". This pattern allows
redirect URIs from any host residing in the domain example.com. So redirect URIs pointing to any host residing in the domain
if an attacker manages to establish a host or subdomain in somesite.example. So if an attacker manages to establish a host or
"example.com" he can impersonate the legitimate client. Assume the subdomain in somesite.example he can impersonate the legitimate
attacker sets up the host "evil.example.com". client. Assume the attacker sets up the host
"evil.somesite.example".
(1) The attacker needs to trick the user into opening a tampered URL (1) The attacker needs to trick the user into opening a tampered URL
in his browser, which launches a page under the attacker's in his browser, which launches a page under the attacker's
control, say "https://www.evil.com". control, say "https://www.evil.example".
(2) This URL initiates an authorization request with the client id (2) This URL initiates an authorization request with the client id
of a legitimate client to the authorization endpoint. This is of a legitimate client to the authorization endpoint. This is
the example authorization request (line breaks are for display the example authorization request (line breaks are for display
purposes only): purposes only):
GET /authorize?response_type=code&client_id=s6BhdRkqt3&state=xyz GET /authorize?response_type=code&client_id=s6BhdRkqt3&state=xyz
&redirect_uri=https%3A%2F%2Fevil.example.com%2Fcb HTTP/1.1 &redirect_uri=https%3A%2F%2Fevil.somesite.example%2Fcb HTTP/1.1
Host: server.example.com Host: server.somesite.example
(1) The authorization validates the redirect URI in order to (3) The authorization server validates the redirect URI in order to
identify the client. Since the pattern allows arbitrary domains identify the client. Since the pattern allows arbitrary domains
host names in "example.com", the authorization request is host names in "somesite.example", the authorization request is
processed under the legitimate client's identity. This includes processed under the legitimate client's identity. This includes
the way the request for user consent is presented to the user. the way the request for user consent is presented to the user.
If auto-approval is allowed (which is not recommended for public If auto-approval is allowed (which is not recommended for public
clients according to RFC 6749), the attack can be performed even clients according to [RFC6749]), the attack can be performed
easier. even easier.
(2) If the user does not recognize the attack, the code is issued (4) If the user does not recognize the attack, the code is issued
and directly sent to the attacker's client. and directly sent to the attacker's client.
(3) Since the attacker impersonated a public client, it can directly (5) Since the attacker impersonated a public client, it can directly
exchange the code for tokens at the respective token endpoint. exchange the code for tokens at the respective token endpoint.
Note: This attack will not directly work for confidential clients, Note: This attack will not directly work for confidential clients,
since the code exchange requires authentication with the legitimate since the code exchange requires authentication with the legitimate
client's secret. The attacker will need to utilize the legitimate client's secret. The attacker will need to utilize the legitimate
client to redeem the code (e.g. by performing a code injection client to redeem the code (e.g., by performing a code injection
attack). This kind of injections is covered in attack). This kind of injections is covered in
Section Code Injection. Section Code Injection.
3.1.2. Attacks on Implicit Grant 3.1.2. Attacks on Implicit Grant
The attack described above works for the implicit grant as well. If The attack described above works for the implicit grant as well. If
the attacker is able to send the authorization response to a URI the attacker is able to send the authorization response to a URI
under his control, he will directly get access to the fragment under his control, he will directly get access to the fragment
carrying the access token. carrying the access token.
Additionally, implicit clients can be subject to a further kind of Additionally, implicit clients can be subject to a further kind of
attacks. It utilizes the fact that user agents re-attach fragments attacks. It utilizes the fact that user agents re-attach fragments
to the destination URL of a redirect if the location header does not to the destination URL of a redirect if the location header does not
contain a fragment (see [RFC7231], section 9.5). The attack contain a fragment (see [RFC7231], Section 9.5). The attack
described here combines this behavior with the client as an open described here combines this behavior with the client as an open
redirector in order to get access to access tokens. This allows redirector in order to get access to access tokens. This allows
circumvention even of strict redirect URI patterns (but not strict circumvention even of strict redirect URI patterns (but not strict
URL matching!). URL matching!).
Assume the pattern for client "s6BhdRkqt3" is Assume the pattern for client "s6BhdRkqt3" is
"https://client.example.com/cb?*", i.e. any parameter is allowed for "https://client.somesite.example/cb?*", i.e., any parameter is
redirects to "https://client.example.com/cb". Unfortunately, the allowed for redirects to "https://client.somesite.example/cb".
client exposes an open redirector. This endpoint supports a Unfortunately, the client exposes an open redirector. This endpoint
parameter "redirect_to", which takes a target URL and will send the supports a parameter "redirect_to" which takes a target URL and will
browser to this URL using a HTTP 302. send the browser to this URL using an HTTP Location header redirect
302.
(1) Same as above, the attacker needs to trick the user into opening (1) Same as above, the attacker needs to trick the user into opening
a tampered URL in his browser, which launches a page under the a tampered URL in his browser, which launches a page under the
attacker's control, say "https://www.evil.com". attacker's control, say "https://www.evil.example".
(2) The URL initiates an authorization request, which is very (2) The URL initiates an authorization request, which is very
similar to the attack on the code flow. As differences, it similar to the attack on the code flow. As differences, it
utilizes the open redirector by encoding utilizes the open redirector by encoding
"redirect_to=https://client.evil.com" into the redirect URI and "redirect_to=https://client.evil.example" into the redirect URI
it uses the response type "token" (line breaks are for display and it uses the response type "token" (line breaks are for
purposes only): display purposes only):
GET /authorize?response_type=token&client_id=s6BhdRkqt3&state=xyz GET /authorize?response_type=token&client_id=s6BhdRkqt3&state=xyz
&redirect_uri=https%3A%2F%2Fclient.example.com%2Fcb%26redirect_to &redirect_uri=https%3A%2F%2Fclient.somesite.example%2Fcb%26redirect_to
%253Dhttps%253A%252F%252Fclient.evil.com%252Fcb HTTP/1.1 %253Dhttps%253A%252F%252Fclient.evil.example%252Fcb HTTP/1.1
Host: server.example.com Host: server.somesite.example
(1) Since the redirect URI matches the registered pattern, the (3) Since the redirect URI matches the registered pattern, the
authorization server allows the request and sends the resulting authorization server allows the request and sends the resulting
access token with a 302 redirect (some response parameters are access token with a 302 redirect (some response parameters are
omitted for better readability) omitted for better readability)
HTTP/1.1 302 Found HTTP/1.1 302 Found
Location: https://client.example.com/cb? Location: https://client.somesite.example/cb?
redirect_to%3Dhttps%3A%2F%2Fclient.evil.com%2Fcb redirect_to%3Dhttps%3A%2F%2Fclient.evil.example%2Fcb
#access_token=2YotnFZFEjr1zCsicMWpAA&... #access_token=2YotnFZFEjr1zCsicMWpAA&...
(2) At the example.com, the request arrives at the open redirector. (4) At the example.com, the request arrives at the open redirector.
It will read the redirect parameter and will issue a HTTP 302 to It will read the redirect parameter and will issue an HTTP 302
the URL "https://evil.example.com/cb". Location header redirect to the URL "https://evil.example.com/
cb".
HTTP/1.1 302 Found HTTP/1.1 302 Found
Location: https://client.evil.com/cb Location: https://client.evil.example/cb
(3) Since the redirector at example.com does not include a fragment (5) Since the redirector at client.somesite.example does not include
in the Location header, the user agent will re-attach the a fragment in the Location header, the user agent will re-attach
original fragment the original fragment
"#access_token=2YotnFZFEjr1zCsicMWpAA&..." to the URL and will "#access_token=2YotnFZFEjr1zCsicMWpAA&..." to the URL and will
navigate to the following URL: navigate to the following URL:
https://client.evil.com/cb#access_token=2YotnFZFEjr1zCsicMWpAA&... https://client.evil.example/cb#access_token=2YotnFZFEjr1zCsicMWpAA&...
(4) The attacker's page at client.evil.com can access the fragment (6) The attacker's page at client.evil.example can access the
and obtain the access token. fragment and obtain the access token.
3.1.3. Proposed Countermeasures 3.1.3. Proposed Countermeasures
The complexity of implementing and managing pattern matching The complexity of implementing and managing pattern matching
correctly obviously causes security issues. This document therefore correctly obviously causes security issues. This document therefore
proposes to simplify the required logic and configuration by using proposes to simplify the required logic and configuration by using
exact redirect URI matching only. This means the authorization exact redirect URI matching only. This means the authorization
server shall compare the two URIs using simple string comparison as server shall compare the two URIs using simple string comparison as
defined in [RFC3986], Section 6.2.1.. defined in [RFC3986], Section 6.2.1..
This would cause the following impacts:
o This change will require all OAuth clients to maintain the
transaction state (and XSRF tokens) in the "state" parameter.
This is a normative change to RFC 6749 since section 3.1.2.2
allows for dynamic URI query parameters in the redirect URI. In
order to assess the practical impact, the working group needs to
collect data on whether this feature is really used in deployments
today.
o The working group may also consider this change as a step towards
improved interoperability for OAuth implementations since RFC 6749
is somewhat vague on redirect URI validation. Notably there are
no rules for pattern matching. One may therefore assume all
clients utilizing pattern matching will do so in a deployment
specific way. On the other hand, RFC 6749 already recommends
exact matching if the full URL had been registered.
o Clients with multiple redirect URIs need to register all of them
explicitly.
Note: clients with just a single redirect URI would not even need
to send a redirect URI with the authorization request. Does it
make sense to emphasize this option? Would that further simplify
use of the protocol and foster security?
o Exact redirect matching does not work for native apps utilizing a
local web server due to dynamic port numbers - at least wild cards
for port numbers are required.
Question: Does redirect uri validation solve any problem for
native apps? Effective against impersonation when used in
conjunction with claimed HTTPS redirect URIs only.
For Windows token broker exact redirect URI matching is important
as the redirect URI encodes the app identity. For custom scheme
redirects there is a question however it is probably a useful part
of defense in depth.
Additional recommendations: Additional recommendations:
o Servers on which callbacks are hosted must not expose open o Servers on which callbacks are hosted must not expose open
redirectors (see Section 3.8). redirectors (see Section 3.8).
o Clients may drop fragments via intermediary URLs with "fix o Clients may drop fragments via intermediary URLs with "fix
fragments" (e.g. https://developers.facebook.com/blog/post/552/) fragments" (see [fb_fragments]) to prevent the user agent from
to prevent the user agent from appending any unintended fragments. appending any unintended fragments.
Alternatives to exact redirect URI matching: As an alternative to exact redirect URI matching, the AS could also
authenticate clients, e.g., using [I-D.ietf-oauth-jwsreq].
o Authenticate clients using digital signatures (see 3.2. Code or State Leakage from Client or AS via Referrer Headers
[I-D.ietf-oauth-jwsreq])
3.2. Authorization code leakage via referrer headers Authorization codes or values of "state" can unintentionally be
disclosed to attackers through the referrer header, by leaking either
from a client's web site or from an AS's web site.
It is possible authorization codes are unintentionally disclosed to Leakage from OAuth client: This requires that the client, as a result
attackers, if a OAuth client renders a page containing links to other of a successful authorization request, renders a page that
pages (ads, faq, ...) as result of a successful authorization
request.
If the user clicks onto one of those links and the target is under o contains links to other pages under the attacker's control (ads,
the control of an attacker, it can get access to the response URL in faq, ...) and a user clicks on such a link, or
the referrer header.
It is also possible that an attacker injects cross-domain content o includes third-party content (iframes, images, etc.) for example
somehow into the page, such as <img> (e.g if this is a blog web if the page contains user-generated content (blog).
site). The implication is obviously the same: loading this content
by browser results in leaking referrer with a code. As soon as the browser navigates to the attacker's page or loads the
third-party content, the attacker receives the authorization response
URL and can extract "code" or "state".
Leakage from AS: In a similar way, an attacker can learn "state" if
the authorization endpoint at the authorization server contains links
or third-party content as above.
Consequences: An attacker that learns a valid code through a referrer
header can perform the same attacks as described in
Section Section 3.1.1. If the attacker learns "state", the CSRF
protection achieved by using "state" is lost, resulting in CSRF
attacks as described in [RFC6819], Section 4.4.1.8..
3.2.1. Proposed Countermeasures 3.2.1. Proposed Countermeasures
There are some means to prevent leakage as described above: The page rendered as a result of the OAuth authorization response and
the authorization endpoint SHOULD not include third-party resources
or links to external sites.
o Make authorization codes one-time use. For example, if the The following measures further reduce the chances of a successful
legitimate client redeemed and invalidated the code in the above attack:
scenario, the attacker would fail exchanging this code later.
o Authorization codes SHOULD be invalidated by the AS after their
first use at the token endpoint. For example, if an AS
invalidated the code after the legitimate client redeemed it, the
attacker would fail exchanging this code later. (This does not
mitigate the attack if the attacker manages to exchange the code
for a token before the legitimate client does so.)
o The "state" value SHOULD be invalidated by the client after its
first use at the redirection endpoint. If this is implemented,
and an attacker receives a token through the referrer header from
the client's web site, the "state" was already used, invalidated
by the client and cannot be used again by the attacker. (This
does not help if the "state" leaks from the AS's web site, since
then the "state" has not been used at the redirection endpoint at
the client yet.)
o Bind authorization code to a confidential client or PKCE o Bind authorization code to a confidential client or PKCE
challenge. In this case, the attacker lacks the secret to request challenge. In this case, the attacker lacks the secret to request
the code exchange. the code exchange.
o Don't include links to external sites into the page rendered as o Suppress the referrer header by adding the attribute
result of a OAuth authorization response "rel="noreferrer"" to HTML links or by applying an appropriate
Referrer Policy [webappsec-referrer-policy] to the document
o Use of the HTML link attribute rel="noreferrer" to suppress (either as part of the "referrer" meta attribute or by setting a
referrer header Referrer-Policy header).
o Use of the "referrer" meta link attribute to suppress referrer
header (see [webappsec-referrer-policy])
o Use form post response mode instead of redirect for authorization o Use form post response mode instead of redirect for authorization
response (see [oauth-v2-form-post-response-mode]) response (see [oauth-v2-form-post-response-mode]).
3.3. Attacks in the Browser 3.3. Attacks through the Browser History
3.3.1. Code in browser history Authorization codes and access tokens can end up in the browser's
history of visited URLs, enabling the attacks described in the
following.
3.3.1. Code in Browser History
When a browser navigates to "client.com/ When a browser navigates to "client.com/
redirection_endpoint?code=abcd" as a result of a redirect from a redirection_endpoint?code=abcd" as a result of a redirect from a
provider's authorization endpoint, the URL including the provider's authorization endpoint, the URL including the
authorization code may end up in the browser's history. An attacker authorization code may end up in the browser's history. An attacker
with access to the device could obtain the code and try to replay it. with access to the device could obtain the code and try to replay it.
Proposed countermeasures: Proposed countermeasures:
o Authorization code replay prevention as described in [RFC6819], o Authorization code replay prevention as described in [RFC6819],
section 4.4.1.1, and Section 3.5 Section 4.4.1.1, and Section 3.5
o Use form post response mode instead of redirect for authorization o Use form post response mode instead of redirect for authorization
response (see [oauth-v2-form-post-response-mode]) response (see [oauth-v2-form-post-response-mode])
3.3.2. Access token in browser history 3.3.2. Access Token in Browser History
An access token may end up in the browser history if a a client or An access token may end up in the browser history if a a client or
just a web site, which already has a token, deliberately navigates to just a web site, which already has a token, deliberately navigates to
a page like "provider.com/get_user_profile?access_token=abcdef.". a page like "provider.com/get_user_profile?access_token=abcdef.".
Actually [RFC6750]discourages this practice and asks to transfer Actually [RFC6750]discourages this practice and asks to transfer
tokens via a header, but in practice web sites often just pass access tokens via a header, but in practice web sites often just pass access
token in query parameters. token in query parameters.
In case of implicit grant, a URL like "client.com/ In case of implicit grant, a URL like "client.com/
redirection_endpoint#access_token=abcdef" may also end up in the redirection_endpoint#access_token=abcdef" may also end up in the
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Proposed countermeasures: Proposed countermeasures:
o Replace implicit flow with postmessage communication or the o Replace implicit flow with postmessage communication or the
authorization code grant authorization code grant
o Never pass access tokens in URL query parameters o Never pass access tokens in URL query parameters
3.4. Mix-Up 3.4. Mix-Up
Mix-up is another kind of attack on more dynamic OAuth scenarios (or Mix-up is an attack on scenarios where an OAuth client interacts with
at least scenarios where a OAuth client interacts with multiple multiple authorization servers, as is usually the case when dynamic
authorization servers). The goal of the attack is to obtain an registration is used. The goal of the attack is to obtain an
authorization code or an access token by tricking the client into authorization code or an access token by tricking the client into
sending those credentials to the attacker (which acts as MITM between sending those credentials to the attacker instead of using them at
client and authorization server) the respective endpoint at the authorization/resource server.
A detailed description of the attack and potential countermeasures is 3.4.1. Attack Description
given in [I-D.ietf-oauth-mix-up-mitigation].
Potential mitigations: For a detailed attack description, refer to [arXiv.1601.01229] and
[I-D.ietf-oauth-mix-up-mitigation]. The description here closely
follows [arXiv.1601.01229], with variants of the attack outlined
below.
o Clients use AS-specific redirect URIs and, for every authorization Preconditions: For the attack to work, we assume that
request, store intended AS and compare intention with actual
redirect URI where the response was received
o AS returns client_id and its iss in the response. Client compares (1) the implicit or authorization code grant are used with multiple
this data to AS it believed it sent the user agent to. AS of which one is considered "honest" (H-AS) and one is
operated by the attacker (A-AS),
o ID token carries client id and issuer (OpenID Connect specific) (2) the client stores the AS chosen by the user in a session bound
to the user's browser and uses the same redirection endpoint URI
for each AS, and
(3) the attacker can manipulate the first request/response pair from
a user's browser to the client (in which the user selects a
certain AS and is then redirected by the client to that AS).
Some of the attack variants described below require different
preconditions.
In the following, we assume that the client is registered with H-AS
(URI: "https://honest.as.example", client id: 7ZGZldHQ) and with A-AS
(URI: "https://attacker.example", client id: 666RVZJTA).
Attack on the authorization code grant:
(1) The user selects to start the grant using H-AS (e.g., by
clicking on a button at the client's website).
(2) The attacker intercepts this request and changes the user's
selection to "A-AS".
(3) The client stores in the user's session that the user selected
"A-AS" and redirects the user to A-AS's authorization endpoint
by sending the following response:
HTTP/1.1 302 Found
Location: https://attacker.example/authorize?response_type=code&client_id=666RVZJTA
(4) Now the attacker intercepts this response and changes the
redirection such that the user is being redirected to H-AS. The
attacker also replaces the client id of the client at A-AS with
the client's id at H-AS, resulting in the following response
being sent to the browser:
HTTP/1.1 302 Found
Location: https://honest.as.example/authorize?response_type=code&client_id=7ZGZldHQ
(5) Now, the user authorizes the client to access her resources at
H-AS. H-AS issues a code and sends it (via the browser) back to
the client.
(6) Since the client still assumes that the code was issued by A-AS,
it will try to redeem the code at A-AS's token endpoint.
(7) The attacker therefore obtains code and can either exchange the
code for an access token (for public clients) or perform a code
injection attack as described in Section Section 3.5.
Variants:
Implicit Grant In the implicit grant, the attacker receives an
access token instead of the code; the rest of the attack
works as above.
Mix-Up Without Interception A variant of the above attack works even
if the first request/response pair cannot be intercepted (for
example, because TLS is used to protect these messages):
Here, we assume that the user wants to start the grant using
A-AS (and not H-AS). After the client redirected the user to
the authorization endpoint at A-AS, the attacker immediately
redirects the user to H-AS (changing the client id
"7ZGZldHQ"). (A vigilant user might at this point detect
that she intended to use A-AS instead of H-AS.) The attack
now proceeds exactly as in step 1 of the attack description
above.
Per-AS Redirect URIs If clients use different redirect URIs for
different ASs, do not store the selected AS in the user's
session, and ASs do not check the redirect URIs properly,
attackers can mount an attack called "Cross-Social Network
Request Forgery". We refer to [oauth_security_jcs_14] for
details.
OpenID Connect There are several variants that can be used to attack
OpenID Connect. They are described in detail in
[arXiv.1704.08539], Appendix A, and [arXiv.1508.04324v2],
Section 6 ("Malicious Endpoints Attacks").
3.4.2. Countermeasures
In scenarios where an OAuth client interacts with multiple
authorization servers, clients MUST prevent mix-up attacks.
Potential countermeasures:
o Configure authorization servers to return an AS identitifier
("iss") and the "client_id" for which a code or token was issued
in the authorization response. This enables clients to compare
this data to their own client id and the "iss" identifier of the
AS it believed it sent the user agent to. This mitigation is
discussed in detail in [I-D.ietf-oauth-mix-up-mitigation]. In
OpenID Connect, if an ID token is returned in the authorization
response, it carries client id and issuer. It can be used for
this mitigation.
o As it can be seen in the preconditions of the attacks above,
clients can prevent mix-up attack by (1) using AS-specific
redirect URIs with exact redirect URI matching, (2) storing, for
each authorization request, the intended AS, and (3) comparing the
intended AS with the actual redirect URI where the authorization
response was received.
3.5. Code Injection 3.5. Code Injection
In such an attack, the adversary attempts to inject a stolen In such an attack, the adversary attempts to inject a stolen
authorization code into a legitimate client on a device under his authorization code into a legitimate client on a device under his
control. In the simplest case, the attacker would want to use the control. In the simplest case, the attacker would want to use the
code in his own client. But there are situations where this might code in his own client. But there are situations where this might
not be possible or intended. Examples are: not be possible or intended. Examples are:
o The attacker wants to access certain functions in this particular o The attacker wants to access certain functions in this particular
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the attacks described above. the attacks described above.
(2) It performs a regular OAuth authorization process with the (2) It performs a regular OAuth authorization process with the
legitimate client on his device. legitimate client on his device.
(3) The attacker injects the stolen authorization code in the (3) The attacker injects the stolen authorization code in the
response of the authorization server to the legitimate client. response of the authorization server to the legitimate client.
(4) The client sends the code to the authorization server's token (4) The client sends the code to the authorization server's token
endpoint, along with client id, client secret and actual endpoint, along with client id, client secret and actual
redirect_uri. "redirect_uri".
(5) The authorization server checks the client secret, whether the (5) The authorization server checks the client secret, whether the
code was issued to the particular client and whether the actual code was issued to the particular client and whether the actual
redirect URI matches the redirect_uri parameter (see [RFC6749]). redirect URI matches the "redirect_uri" parameter (see
[RFC6749]).
(6) If all checks succeed, the authorization server issues access (6) If all checks succeed, the authorization server issues access
and other tokens to the client, so now the attacker is able to and other tokens to the client, so now the attacker is able to
impersonate the legitimate user. impersonate the legitimate user.
Obviously, the check in step (5) will fail, if the code was issued to Obviously, the check in step (5) will fail, if the code was issued to
another client id, e.g. a client set up by the attacker. The check another client id, e.g., a client set up by the attacker. The check
will also fail if the authorization code was already redeemed by the will also fail if the authorization code was already redeemed by the
legitimate user and was one-time use only. legitimate user and was one-time use only.
An attempt to inject a code obtained via a malware pretending to be An attempt to inject a code obtained via a malware pretending to be
the legitimate client should also be detected, if the authorization the legitimate client should also be detected, if the authorization
server stored the complete redirect URI used in the authorization server stored the complete redirect URI used in the authorization
request and compares it with the redirect_uri parameter. request and compares it with the redirect_uri parameter.
[RFC6749], Section 4.1.3, requires the AS to "... ensure that the [RFC6749], Section 4.1.3, requires the AS to "... ensure that the
"redirect_uri" parameter is present if the "redirect_uri" parameter "redirect_uri" parameter is present if the "redirect_uri" parameter
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land at the attackers page). So the authorization server would land at the attackers page). So the authorization server would
detect the attack and refuse to exchange the code. detect the attack and refuse to exchange the code.
Note: this check could also detect attempt to inject a code, which Note: this check could also detect attempt to inject a code, which
had been obtained from another instance of the same client on another had been obtained from another instance of the same client on another
device, if certain conditions are fulfilled: device, if certain conditions are fulfilled:
o the redirect URI itself needs to contain a nonce or another kind o the redirect URI itself needs to contain a nonce or another kind
of one-time use, secret data and of one-time use, secret data and
o the client has bound this data to this particular instance o the client has bound this data to this particular instance.
But this approach conflicts with the idea to enforce exact redirect But this approach conflicts with the idea to enforce exact redirect
URI matching at the authorization endpoint. Moreover, it has been URI matching at the authorization endpoint. Moreover, it has been
observed that providers very often ignore the redirect_uri check observed that providers very often ignore the redirect_uri check
requirement at this stage, maybe, because it doesn't seem to be requirement at this stage, maybe because it doesn't seem to be
security-critical from reading the spec. security-critical from reading the spec.
Other providers just pattern match the redirect_uri parameter against Other providers just pattern match the redirect_uri parameter against
the registered redirect URI pattern. This saves the authorization the registered redirect URI pattern. This saves the authorization
server from storing the link between the actual redirect URI and the server from storing the link between the actual redirect URI and the
respective authorization code for every transaction. But this kind respective authorization code for every transaction. But this kind
of check obviously does not fulfill the intent of the spec, since the of check obviously does not fulfill the intent of the spec, since the
tampered redirect URI is not considered. So any attempt to inject a tampered redirect URI is not considered. So any attempt to inject a
code obtained using the client_id of a legitimate client or by code obtained using the "client_id" of a legitimate client or by
utilizing the legitimate client on another device won't be detected utilizing the legitimate client on another device won't be detected
in the respective deployments. in the respective deployments.
It is also assumed that the requirements defined in [RFC6749], It is also assumed that the requirements defined in [RFC6749],
Section 4.1.3, increase client implementation complexity as clients Section 4.1.3, increase client implementation complexity as clients
need to memorize or re-construct the correct redirect URI for the need to memorize or re-construct the correct redirect URI for the
call to the tokens endpoint. call to the tokens endpoint.
The authors therefore propose to the working group to drop this This document therefore recommends to instead bind every
feature in favor of more effective and (hopefully) simpler approaches authorization code to a certain client instance on a certain device
to code injection prevention as described in the following section. (or in a certain user agent) in the context of a certain transaction.
3.5.1. Proposed Countermeasures 3.5.1. Proposed Countermeasures
The general proposal is to bind every authorization code to a certain There are multiple technical solutions to achieve this goal:
client instance on a certain device (or in a certain user agent) in
the context of a certain transaction. There are multiple technical
solutions to achieve this goal:
Nonce OpenID Connect's existing "nonce" parameter could be used for Nonce OpenID Connect's existing "nonce" parameter could be used for
this purpose. The nonce value is one-time use and created by this purpose. The nonce value is one-time use and created by
the client. The client is supposed to bind it to the user the client. The client is supposed to bind it to the user
agent session and sends it with the initial request to the agent session and sends it with the initial request to the
OpenId Provider (OP). The OP associates the nonce to the OpenId Provider (OP). The OP associates the nonce to the
authorization code and attests this binding in the ID token, authorization code and attests this binding in the ID token,
which is issued as part of the code exchange at the token which is issued as part of the code exchange at the token
endpoint. If an attacker injected an authorization code in endpoint. If an attacker injected an authorization code in
the authorization response, the nonce value in the client the authorization response, the nonce value in the client
session and the nonce value in the ID token will not match session and the nonce value in the ID token will not match
and the attack is detected. assumption: attacker cannot get and the attack is detected. The assumption is that an
hold of the user agent state on the victims device, where he attacker cannot get hold of the user agent state on the
has stolen the respective authorization code. The main victims device, where he has stolen the respective
advantage of this option is that Nonce is an existing feature authorization code. The main advantage of this option is
used in the wild. On the other hand, leveraging Nonce by the that Nonce is an existing feature used in the wild. On the
broader OAuth community would require AS and client to adopt other hand, leveraging Nonce by the broader OAuth community
ID Tokens. would require AS and client to adopt ID Tokens.
Code-bound State The "state" parameter as specified in [RFC6749] Code-bound State The "state" parameter as specified in [RFC6749]
could be used similarly to the way as described above. This could be used similarly to what is described above. This
would require to add a further parameter "state" to the code would require to add a further parameter "state" to the code
exchange token endpoint request. The authorization server exchange token endpoint request. The authorization server
would then compares the state value it associated with the would then compare the "state" value it associated with the
code and the state value in the parameter. If those values code and the "state" value in the parameter. If those values
do not match, it is considered an attack and the request do not match, it is considered an attack and the request
fails. The advantage of this approach would be to utilize an fails. The advantage of this approach would be to utilize an
existing OAuth parameter. But it would also mean to re- existing OAuth parameter. But it would also mean to re-
interpret the purpose of state and to extend the token interpret the purpose of "state" and to extend the token
endpoint request. endpoint request.
PKCE The PKCE parameter "challenge" along with the corresponding PKCE The PKCE parameter "challenge" along with the corresponding
"verifier" as specified in [RFC7636] could be used in the "verifier" as specified in [RFC7636] could be used in the
same way as "nonce" or "state". In contrast to its original same way as "nonce" or "state". In contrast to its original
intention, the verifier check would fail although the client intention, the verifier check would fail although the client
uses its correct verifier but the code is associated with a uses its correct verifier but the code is associated with a
challenge, which does not match. PKCE is a deployed OAuth challenge, which does not match. PKCE is a deployed OAuth
feature, even so it is today used to secure native apps, feature, even though it is used today to secure native apps,
only. only.
Token Binding Token binding [I-D.ietf-oauth-token-binding] could Token Binding Token binding [I-D.ietf-oauth-token-binding] could
also be used. In this case, the code would need to be bound also be used. In this case, the code would need to be bound
to two legs, between user agent and AS and the user agent and to two legs, between user agent and AS and the user agent and
the client. This requires further data (extension to the client. This requires further data (extension to
response) to manifest binding id for particular code. Token response) to manifest binding id for particular code. Token
binding is promising as a secure and convenient mechanism binding is promising as a secure and convenient mechanism
(due to its browser integration). As a challenge, it (due to its browser integration). As a challenge, it
requires broad browser support and use with native apps still requires broad browser support and use with native apps is
under discussion. still under discussion.
per instance client id/secret One could use per instance client_id per instance client id/secret One could use per instance "client_id"
and secrets and bind the code to the respective client_id. and secrets and bind the code to the respective "client_id".
Unfortunately, this does not fit into the web application Unfortunately, this does not fit into the web application
programming model (would need to use per user client ids). programming model (would need to use per user client ids).
PKCE seem to be the most obvious solution for OAuth clients as it PKCE seems to be the most obvious solution for OAuth clients as it
available and effectively used today for similar purposes for OAuth available and effectively used today for similar purposes for OAuth
native apps whereas "nonce" is appropriate for OpenId Connect native apps whereas "nonce" is appropriate for OpenId Connect
clients. clients.
Note on pre-warmed secrets: An attacker can circumvent the Note on pre-warmed secrets: An attacker can circumvent the
countermeasures described above if he is able to create or capture countermeasures described above if he is able to create or capture
the respective secret or code_challenge on a device under his the respective secret or code_challenge on a device under his
control, which is then used in the victim's authorization request. control, which is then used in the victim's authorization request.
Exact redirect URI matching of authorization requests can prevent the Exact redirect URI matching of authorization requests can prevent the
attacker from using the pre-warmed secret in the faked authorization attacker from using the pre-warmed secret in the faked authorization
transaction on the victim's device. transaction on the victim's device.
Unfortunately it does not work for all kinds of OAuth clients. It is Unfortunately, it does not work for all kinds of OAuth clients. It
effective for web and JS apps and for native apps with claimed URLs. is effective for web and JS apps and for native apps with claimed
Attacks on native apps using custom schemes or redirect URIs on URLs. Attacks on native apps using custom schemes or redirect URIs
localhost cannot be prevented this way, except if the AS enforces on localhost cannot be prevented this way, except if the AS enforces
one-time use for PKCE verifier or Nonce values. one-time use for PKCE verifier or "nonce" values.
3.6. Cross Site Request Forgery 3.6. Cross Site Request Forgery
An attacker might attempt to inject a request to the redirect URI of An attacker might attempt to inject a request to the redirect URI of
the legitimate client on the victim's device, e.g. to cause the the legitimate client on the victim's device, e.g., to cause the
client to access resources under the attacker's control. client to access resources under the attacker's control.
Proposed mitigation: use of XSRF tokens (one-time use), which are 3.6.1. Proposed Countermeasures
bound to the user agent and passed in the state parameter to the
authorization server. For more details see [owasp_csrf]. Standard CSRF defenses should be used to protect the redirection
endpoint, for example:
CSRF Tokens Use of CSRF tokens which are bound to the user agent
and passed in the "state" parameter to the
authorization server.
Origin Header The Origin header can be used to detect and prevent
CSRF attacks. Since this feature, at the time of
writing, is not consistently supported by all
browsers, CSRF tokens should be used in addition to
Origin header checking.
For more details see [owasp_csrf].
3.7. Access Token Leakage at the Resource Server 3.7. Access Token Leakage at the Resource Server
Access tokens can leak from a resource server under certain
circumstances.
3.7.1. Access Token Phishing by Counterfeit Resource Server 3.7.1. Access Token Phishing by Counterfeit Resource Server
An attacker may setup his own resource server and trick a client into An attacker may setup his own resource server and trick a client into
sending access tokens to it, which are valid for other resource sending access tokens to it, which are valid for other resource
servers. If the client sends a valid access token to this servers. If the client sends a valid access token to this
counterfeit resource server, the attacker in turn may use that token counterfeit resource server, the attacker in turn may use that token
to access other services on behalf of the resource owner. to access other services on behalf of the resource owner.
This attack assumes the client is not bound to a certain resource This attack assumes the client is not bound to a certain resource
server (and the respective URL) at development time, but client server (and the respective URL) at development time, but client
instances are configured with an resource server's URL at runtime. instances are configured with an resource server's URL at runtime.
This kind of late binding is typical in situations, where the client This kind of late binding is typical in situations where the client
uses a standard API, e.g. for e-Mail, calendar, health, or banking uses a standard API, e.g., for e-Mail, calendar, health, or banking
and is configured by an user or administrator for the standard-based and is configured by an user or administrator for the standard-based
service, this particular user or company uses. service, this particular user or company uses.
There are several potential mitigation strategies, which will be There are several potential mitigation strategies, which will be
discussed in the following sections. discussed in the following sections.
3.7.1.1. Metadata 3.7.1.1. Metadata
An authorization server could provide the client with additional An authorization server could provide the client with additional
information about the location where it is safe to use its access information about the location where it is safe to use its access
tokens. tokens.
In the simplest form, this would require the AS to publish a list of In the simplest form, this would require the AS to publish a list of
its known resource servers, illustrated in the following example its known resource servers, illustrated in the following example
using a metadata parameter "resource_servers": using a metadata parameter "resource_servers":
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json Content-Type: application/json
{ {
"issuer":"https://server.example.com", "issuer":"https://server.somesite.example",
"authorization_endpoint":"https://server.example.com/authorize", "authorization_endpoint":"https://server.somesite.example/authorize",
"resource_servers":[ "resource_servers":[
"email.example.com", "email.somesite.example",
"storage.example.com", "storage.somesite.example",
"video.example.com"] "video.somesite.example"]
... ...
} }
The AS could also return the URL(s) an access token is good for in The AS could also return the URL(s) an access token is good for in
the token response, illustrated by the example return parameter the token response, illustrated by the example return parameter
"access_token_resource_server": "access_token_resource_server":
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8 Content-Type: application/json;charset=UTF-8
Cache-Control: no-store Cache-Control: no-store
Pragma: no-cache Pragma: no-cache
{ {
"access_token":"2YotnFZFEjr1zCsicMWpAA", "access_token":"2YotnFZFEjr1zCsicMWpAA",
"access_token_resource_server":"https://hostedresource.example.com/path1", "access_token_resource_server":"https://hostedresource.somesite.example/path1",
... ...
} }
This mitigation strategy would rely on the client to enforce the This mitigation strategy would rely on the client to enforce the
security policy and to only send access tokens to legitimate security policy and to only send access tokens to legitimate
destinations. Results of OAuth related security research (see for destinations. Results of OAuth related security research (see for
example [oauth_security_ubc] and [oauth_security_cmu]) indicate a example [oauth_security_ubc] and [oauth_security_cmu]) indicate a
large portion of client implementations do not or fail to properly large portion of client implementations do not or fail to properly
implement security controls, like state checks. So relying on implement security controls, like "state" checks. So relying on
clients to prevent access token phishing is likely to fail as well. clients to prevent access token phishing is likely to fail as well.
Moreover given the ratio of clients to authorization and resource Moreover given the ratio of clients to authorization and resource
servers, it is considered the more viable approach to move as much as servers, it is considered the more viable approach to move as much as
possible security-related logic to those entities. Clearly, the possible security-related logic to those entities. Clearly, the
client has to contribute to the overall security. But there are client has to contribute to the overall security. But there are
alternative counter measures, as described in the next sections, alternative countermeasures, as described in the next sections, which
which provide a better balance between the involved parties. provide a better balance between the involved parties.
3.7.1.2. Sender Constrained Access Tokens 3.7.1.2. Sender Constrained Access Tokens
As the name suggests, sender constraint access token scope the As the name suggests, sender constrained access token scope the
applicability of an access token to a certain sender. This sender is applicability of an access token to a certain sender. This sender is
obliged to demonstrate knowledge of a certain secret as prerequisite obliged to demonstrate knowledge of a certain secret as prerequisite
for the acceptance of that token at a resource server. for the acceptance of that token at a resource server.
A typical flow looks like this: A typical flow looks like this:
1. The authorization server associates data with the access token, 1. The authorization server associates data with the access token
which bind this particular token to a certain client. The which binds this particular token to a certain client. The
binding can utilize the client identity, but in most cases the AS binding can utilize the client identity, but in most cases the AS
utilizes key material (or data derived from the key material) utilizes key material (or data derived from the key material)
known to the client. known to the client.
2. This key material must be distributed somehow. Either the key 2. This key material must be distributed somehow. Either the key
material already exists before the AS creates the binding or the material already exists before the AS creates the binding or the
AS creates ephemeral keys. The way pre-existing key material is AS creates ephemeral keys. The way pre-existing key material is
distributed varies among the different approaches. For example, distributed varies among the different approaches. For example,
X.509 Certificates can be used in which case the distribution X.509 Certificates can be used in which case the distribution
happens explicitly during the enrollment process. Or the key happens explicitly during the enrollment process. Or the key
material is created and distributed at the TLS layer, in which material is created and distributed at the TLS layer, in which
case it might automatically happens during the setup of a TLS case it might automatically happens during the setup of a TLS
connection. connection.
3. The RS must implement the actual proof of possession check. This 3. The RS must implement the actual proof of possession check. This
is typically done on the application level, it may utilize is typically done on the application level, it may utilize
capabilities of the transport layer (e.g. TLS). Note: replay capabilities of the transport layer (e.g., TLS). Note: replay
prevention is required as well! prevention is required as well!
There exists several proposals to demonstrate the proof of possession There exists several proposals to demonstrate the proof of possession
in the scope of the OAuth working group: in the scope of the OAuth working group:
o [I-D.ietf-oauth-token-binding]: In this approach, an access tokens o [I-D.ietf-oauth-token-binding]: In this approach, an access tokens
is, via the so-called token binding id, bound to key material is, via the so-called token binding id, bound to key material
representing a long term association between a client and a representing a long term association between a client and a
certain TLS host. Negotiation of the key material and proof of certain TLS host. Negotiation of the key material and proof of
possession in the context of a TLS handshake is taken care of by possession in the context of a TLS handshake is taken care of by
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short term. short term.
Application level signing approaches, like Application level signing approaches, like
[I-D.ietf-oauth-signed-http-request] and [I-D.sakimura-oauth-jpop] [I-D.ietf-oauth-signed-http-request] and [I-D.sakimura-oauth-jpop]
have been debated for a long time in the OAuth working group without have been debated for a long time in the OAuth working group without
a clear outcome. a clear outcome.
As one advantage, application-level signing allows for end-to-end As one advantage, application-level signing allows for end-to-end
protection including non-repudiation even if the TLS connection is protection including non-repudiation even if the TLS connection is
terminated between client and resource server. But deployment terminated between client and resource server. But deployment
experiences have revealed challenges regarding robustness (e.g. experiences have revealed challenges regarding robustness (e.g.,
reproduction of the signature base string including correct URL) as reproduction of the signature base string including correct URL) as
well as state management (e.g. replay prevention). well as state management (e.g., replay prevention).
This document therefore recommends implementors to consider one of This document therefore recommends implementors to consider one of
TLS-based approaches wherever possible. TLS-based approaches wherever possible.
3.7.1.3. Audience Restricted Access Tokens 3.7.1.3. Audience Restricted Access Tokens
An audience restriction essentially restricts the resource server a An audience restriction essentially restricts the resource server a
particular access token can be used at. The authorization server particular access token can be used at. The authorization server
associates the access token with a certain resource server and every associates the access token with a certain resource server and every
resource server is obliged to verify for every request, whether the resource server is obliged to verify for every request, whether the
skipping to change at page 20, line 39 skipping to change at page 23, line 27
scope of token leakage prevention. It allows the authorization scope of token leakage prevention. It allows the authorization
server to create different access token whose format and content is server to create different access token whose format and content is
specifically minted for the respective server. This has huge specifically minted for the respective server. This has huge
functional and privacy advantages in deployments using structured functional and privacy advantages in deployments using structured
access tokens. access tokens.
3.7.2. Compromised Resource Server 3.7.2. Compromised Resource Server
An attacker may compromise a resource server in order to get access An attacker may compromise a resource server in order to get access
to its resources and other resources of the respective deployment. to its resources and other resources of the respective deployment.
Such a compromise may range from partial access to the system, e.g. Such a compromise may range from partial access to the system, e.g.,
its logfiles, to full control of the respective server. its logfiles, to full control of the respective server.
If the attacker was able to take over full control including shell If the attacker was able to take over full control including shell
access it will be able to circumvent all controls in place and access access it will be able to circumvent all controls in place and access
resources without access control. It will also get access to access resources without access control. It will also get access to access
tokens, which are sent to the compromised system and which tokens, which are sent to the compromised system and which
potentially are valid for access to other resource servers as well. potentially are valid for access to other resource servers as well.
Even if the attacker "only" is able to access logfiles or databases Even if the attacker "only" is able to access logfiles or databases
of the server system, it may get access to valid access tokens. of the server system, it may get access to valid access tokens.
skipping to change at page 21, line 27 skipping to change at page 24, line 17
other resource servers. Depending on the severity of the other resource servers. Depending on the severity of the
penetration, it will also prevent replay on the compromised penetration, it will also prevent replay on the compromised
system. system.
o Audience restriction as described in Section 3.7.1.3 may be used o Audience restriction as described in Section 3.7.1.3 may be used
to prevent replay of captured access tokens on other resource to prevent replay of captured access tokens on other resource
servers. servers.
3.8. Open Redirection 3.8. Open Redirection
The following attacks can occur when an AS or client has an open
redirector, i.e., a URL which causes an HTTP redirect to an attacker-
controlled web site.
3.8.1. Authorization Server as Open Redirector 3.8.1. Authorization Server as Open Redirector
Attackers could try to utilize a user's trust in the authorization Attackers could try to utilize a user's trust in the authorization
server (and its URL in particular) for performing phishing attacks. server (and its URL in particular) for performing phishing attacks.
The attacker could send an authorization request with an invalid
combination of client_id and redirect_uri. [RFC6749], section
4.1.2.1, already states that the AS MUST NOT automatically redirect
the user agent in this case to prevent open redirection.
But as described in [I-D.ietf-oauth-closing-redirectors], the [RFC6749], Section 4.1.2.1, already prevents open redirects by
attacker could also attempt to register a client and intentionally stating the AS MUST NOT automatically redirect the user agent in case
send an erroneous authorization request, e.g. by using an invalid of an invalid combination of client_id and redirect_uri.
scope value. According to [RFC6749], the AS would send the user
agent to the redirect_uri with an "invalid_request" error response. However, as described in [I-D.ietf-oauth-closing-redirectors], an
This is dangerous because the authorization server would serve as an attacker could also utilize a correctly registered redirect URI to
open redirector. Therefore this draft recommends that every invalid perform phishing attacks. It could for example register a client via
authorization request MUST NOT automatically redirect the user agent dynamic client [RFC7591] registration and intentionally send an
to the client's redirect URI. erroneous authorization request, e.g., by using an invalid scope
value, to cause the AS to automatically redirect the user agent to
its phishing site.
The AS MUST take precautions to prevent this threat. Based on its
risk assessment the AS needs to decide whether it can trust the
redirect URI or not and SHOULD only automatically redirect the user
agent, if it trusts the redirect URI. If not, it MAY inform the user
that it is about to redirect her to the another site and rely on the
user to decide or MAY just inform the user about the error.
3.8.2. Clients as Open Redirector 3.8.2. Clients as Open Redirector
Client MUST not expose URLs which could be utilized as open Client MUST not expose URLs which could be utilized as open
redirector. An open redirector is a way to cause the recipient of a redirector. Attackers may use an open redirector to produce URLs
HTTP request to issue a redirect to a target URL that is passed as a
parameter. Attackers may utilize such a mechanism to produce URLs,
which appear to point to the client, which might trick users to trust which appear to point to the client, which might trick users to trust
the URL and follow it in her browser. Another abuse case is to the URL and follow it in her browser. Another abuse case is to
produce URLs pointing to the client and utilize them to impersonate a produce URLs pointing to the client and utilize them to impersonate a
client with an authorization server. client with an authorization server.
In order to prevent open redirection, clients should only expose such In order to prevent open redirection, clients should only expose such
a function, if the target URLs are whitelisted or if the origin of a a function, if the target URLs are whitelisted or if the origin of a
request can be authenticated. request can be authenticated.
3.9. TLS Terminating Reverse Proxies 3.9. TLS Terminating Reverse Proxies
skipping to change at page 23, line 8 skipping to change at page 25, line 49
between proxy and application server, it could also try to circumvent between proxy and application server, it could also try to circumvent
security controls in place. It is therefore important to ensure the security controls in place. It is therefore important to ensure the
authenticity of the communicating entities. Furthermore, the authenticity of the communicating entities. Furthermore, the
communication link between reverse proxy and application server must communication link between reverse proxy and application server must
therefore be protected against tapping and injection (including therefore be protected against tapping and injection (including
replay prevention). replay prevention).
4. Acknowledgements 4. Acknowledgements
We would like to thank Jim Manico, Phil Hunt, Nat Sakimura, Christian We would like to thank Jim Manico, Phil Hunt, Nat Sakimura, Christian
Mainka, and Brian Campbell for their valuable feedback. Mainka, Doug McDorman, and Brian Campbell for their valuable
feedback.
5. IANA Considerations 5. IANA Considerations
This draft includes no request to IANA. This draft includes no request to IANA.
6. Security Considerations 6. Security Considerations
All relevant security considerations have been given in the All relevant security considerations have been given in the
functional specification. functional specification.
skipping to change at page 24, line 7 skipping to change at page 27, line 5
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and [RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol", P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015, RFC 7591, DOI 10.17487/RFC7591, July 2015,
<https://www.rfc-editor.org/info/rfc7591>. <https://www.rfc-editor.org/info/rfc7591>.
7.2. Informative References 7.2. Informative References
[arXiv.1508.04324v2]
Mladenov, V., Mainka, C., and J. Schwenk, "On the security
of modern Single Sign-On Protocols: Second-Order
Vulnerabilities in OpenID Connect", arXiv 1508.04324v2,
January 2016, <http://arxiv.org/abs/1508.04324v2/>.
[arXiv.1601.01229]
Fett, D., Kuesters, R., and G. Schmitz, "A Comprehensive
Formal Security Analysis of OAuth 2.0", arXiv 1601.01229,
January 2016, <http://arxiv.org/abs/1601.01229/>.
[arXiv.1704.08539]
Fett, D., Kuesters, R., and G. Schmitz, "The Web SSO
Standard OpenID Connect: In-Depth Formal Security Analysis
and Security Guidelines", arXiv 1704.08539, April 2017,
<http://arxiv.org/abs/1704.08539/>.
[fb_fragments]
"Facebook Developer Blog",
<https://developers.facebook.com/blog/post/552/>.
[I-D.bradley-oauth-jwt-encoded-state] [I-D.bradley-oauth-jwt-encoded-state]
Bradley, J., Lodderstedt, T., and H. Zandbelt, "Encoding Bradley, J., Lodderstedt, T., and H. Zandbelt, "Encoding
claims in the OAuth 2 state parameter using a JWT", draft- claims in the OAuth 2 state parameter using a JWT", draft-
bradley-oauth-jwt-encoded-state-08 (work in progress), bradley-oauth-jwt-encoded-state-08 (work in progress),
January 2018. January 2018.
[I-D.campbell-oauth-resource-indicators] [I-D.campbell-oauth-resource-indicators]
Campbell, B., Bradley, J., and H. Tschofenig, "Resource Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", draft-campbell-oauth-resource- Indicators for OAuth 2.0", draft-campbell-oauth-resource-
indicators-02 (work in progress), November 2016. indicators-02 (work in progress), November 2016.
skipping to change at page 24, line 32 skipping to change at page 27, line 51
2016. 2016.
[I-D.ietf-oauth-discovery] [I-D.ietf-oauth-discovery]
Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0 Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", draft-ietf-oauth- Authorization Server Metadata", draft-ietf-oauth-
discovery-10 (work in progress), March 2018. discovery-10 (work in progress), March 2018.
[I-D.ietf-oauth-jwsreq] [I-D.ietf-oauth-jwsreq]
Sakimura, N. and J. Bradley, "The OAuth 2.0 Authorization Sakimura, N. and J. Bradley, "The OAuth 2.0 Authorization
Framework: JWT Secured Authorization Request (JAR)", Framework: JWT Secured Authorization Request (JAR)",
draft-ietf-oauth-jwsreq-15 (work in progress), July 2017. draft-ietf-oauth-jwsreq-16 (work in progress), April 2018.
[I-D.ietf-oauth-mix-up-mitigation] [I-D.ietf-oauth-mix-up-mitigation]
Jones, M., Bradley, J., and N. Sakimura, "OAuth 2.0 Mix-Up Jones, M., Bradley, J., and N. Sakimura, "OAuth 2.0 Mix-Up
Mitigation", draft-ietf-oauth-mix-up-mitigation-01 (work Mitigation", draft-ietf-oauth-mix-up-mitigation-01 (work
in progress), July 2016. in progress), July 2016.
[I-D.ietf-oauth-mtls] [I-D.ietf-oauth-mtls]
Campbell, B., Bradley, J., Sakimura, N., and T. Campbell, B., Bradley, J., Sakimura, N., and T.
Lodderstedt, "OAuth 2.0 Mutual TLS Client Authentication Lodderstedt, "OAuth 2.0 Mutual TLS Client Authentication
and Certificate Bound Access Tokens", draft-ietf-oauth- and Certificate Bound Access Tokens", draft-ietf-oauth-
mtls-07 (work in progress), January 2018. mtls-08 (work in progress), May 2018.
[I-D.ietf-oauth-pop-key-distribution] [I-D.ietf-oauth-pop-key-distribution]
Bradley, J., Hunt, P., Jones, M., and H. Tschofenig, Bradley, J., Hunt, P., Jones, M., and H. Tschofenig,
"OAuth 2.0 Proof-of-Possession: Authorization Server to "OAuth 2.0 Proof-of-Possession: Authorization Server to
Client Key Distribution", draft-ietf-oauth-pop-key- Client Key Distribution", draft-ietf-oauth-pop-key-
distribution-03 (work in progress), February 2017. distribution-03 (work in progress), February 2017.
[I-D.ietf-oauth-signed-http-request] [I-D.ietf-oauth-signed-http-request]
Richer, J., Bradley, J., and H. Tschofenig, "A Method for Richer, J., Bradley, J., and H. Tschofenig, "A Method for
Signing HTTP Requests for OAuth", draft-ietf-oauth-signed- Signing HTTP Requests for OAuth", draft-ietf-oauth-signed-
http-request-03 (work in progress), August 2016. http-request-03 (work in progress), August 2016.
[I-D.ietf-oauth-token-binding] [I-D.ietf-oauth-token-binding]
Jones, M., Campbell, B., Bradley, J., and W. Denniss, Jones, M., Campbell, B., Bradley, J., and W. Denniss,
"OAuth 2.0 Token Binding", draft-ietf-oauth-token- "OAuth 2.0 Token Binding", draft-ietf-oauth-token-
binding-06 (work in progress), March 2018. binding-06 (work in progress), March 2018.
[I-D.ietf-tokbind-https] [I-D.ietf-tokbind-https]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., Harper, Popov, A., Nystrom, M., Balfanz, D., Langley, A., Harper,
N., and J. Hodges, "Token Binding over HTTP", draft-ietf- N., and J. Hodges, "Token Binding over HTTP", draft-ietf-
tokbind-https-12 (work in progress), January 2018. tokbind-https-14 (work in progress), May 2018.
[I-D.sakimura-oauth-jpop] [I-D.sakimura-oauth-jpop]
Sakimura, N., Li, K., and J. Bradley, "The OAuth 2.0 Sakimura, N., Li, K., and J. Bradley, "The OAuth 2.0
Authorization Framework: JWT Pop Token Usage", draft- Authorization Framework: JWT Pop Token Usage", draft-
sakimura-oauth-jpop-04 (work in progress), March 2017. sakimura-oauth-jpop-04 (work in progress), March 2017.
[oauth-v2-form-post-response-mode] [oauth-v2-form-post-response-mode]
Microsoft and Ping Identity, "OAuth 2.0 Form Post Response Microsoft and Ping Identity, "OAuth 2.0 Form Post Response
Mode", April 2015, <http://openid.net/specs/ Mode", April 2015, <http://openid.net/specs/
oauth-v2-form-post-response-mode-1_0.html>. oauth-v2-form-post-response-mode-1_0.html>.
[oauth_security_cmu] [oauth_security_cmu]
Carnegie Mellon University, Carnegie Mellon University, Carnegie Mellon University, Carnegie Mellon University,
Microsoft Research, Carnegie Mellon University, Carnegie Microsoft Research, Carnegie Mellon University, Carnegie
Mellon University, and Carnegie Mellon University, "OAuth Mellon University, and Carnegie Mellon University, "OAuth
Demystified for Mobile Application Developers", November Demystified for Mobile Application Developers", November
2014. 2014.
[oauth_security_jcs_14]
Bansal, C., Bhargavan, K., Delignat-Lavaud, A., and S.
Maffeis, "Discovering concrete attacks on website
authorization by formal analysis", April 2014.
[oauth_security_ubc] [oauth_security_ubc]
University of British Columbia and University of British University of British Columbia and University of British
Columbia, "The Devil is in the (Implementation) Details: Columbia, "The Devil is in the (Implementation) Details:
An Empirical Analysis of OAuth SSO Systems", October 2012, An Empirical Analysis of OAuth SSO Systems", October 2012,
<http://passwordresearch.com/papers/paper267.html>. <http://passwordresearch.com/papers/paper267.html>.
[OpenID] NRI, Ping Identity, Microsoft, Google, and Salesforce, [OpenID] NRI, Ping Identity, Microsoft, Google, and Salesforce,
"OpenID Connect Core 1.0 incorporating errata set 1", Nov "OpenID Connect Core 1.0 incorporating errata set 1", Nov
2014, 2014,
<http://openid.net/specs/openid-connect-core-1_0.html>. <http://openid.net/specs/openid-connect-core-1_0.html>.
skipping to change at page 26, line 28 skipping to change at page 29, line 47
<https://www.rfc-editor.org/info/rfc7800>. <https://www.rfc-editor.org/info/rfc7800>.
[webappsec-referrer-policy] [webappsec-referrer-policy]
Google Inc. and Google Inc., "Referrer Policy", April Google Inc. and Google Inc., "Referrer Policy", April
2017, <https://w3c.github.io/webappsec-referrer-policy>. 2017, <https://w3c.github.io/webappsec-referrer-policy>.
Appendix A. Document History Appendix A. Document History
[[ To be removed from the final specification ]] [[ To be removed from the final specification ]]
-06
o reworked section 3.8.1
o incorporated Phil Hunt's feedback
o reworked section on mix-up
o extended section on code leakage via referrer header to also cover
state leakage
o added Daniel Fett as author
o replaced text intended to inform WG discussion by recommendations
to implementors
o modified example URLs to conform to RFC 2606
-05 -05
o Completed sections on code leakage via referrer header, attacks in o Completed sections on code leakage via referrer header, attacks in
browser, mix-up, and CSRF browser, mix-up, and CSRF
o Reworked Code Injection Section o Reworked Code Injection Section
o Added reference to OpenID Connect spec o Added reference to OpenID Connect spec
o removed refresh token leakage as respective considerations have o removed refresh token leakage as respective considerations have
skipping to change at line 1280 skipping to change at page 31, line 34
John Bradley John Bradley
Yubico Yubico
Email: ve7jtb@ve7jtb.com Email: ve7jtb@ve7jtb.com
Andrey Labunets Andrey Labunets
Facebook Facebook
Email: isciurus@fb.com Email: isciurus@fb.com
Daniel Fett
University of Stuttgart
Email: daniel.fett@sec.uni-stuttgart.de
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