CVE-2022-39222
ADVISORY - githubSummary
Impact
Dex instances with public clients (and by extension, clients accepting tokens issued by those Dex instances) are affected by this vulnerability.
An attacker can exploit this vulnerability by making a victim navigate to a malicious website and guiding them through the OIDC flow, stealing the OAuth authorization code in the process. The authorization code then can be exchanged by the attacker for a token, gaining access to applications accepting that token.
Steps to reproduce
A victim navigates to a malicious website
The webserver initiates a connection with a Dex instance directly - https://dexexample.com/auth/https:%252F%252Faccounts.google.com?access_type=online&client_id=example&nonce=2AaJAimQU9CbeOFsNra1d7CJTWB&redirect_uri=http%3A%2F%2Flocalhost%3A40393%2Fauth%2Fcallback&response_type=code&scope=openid+email&state=2AaJAjhpUmsB25csCo5muvorMTl. In this example, the Dex instance is hosted on
dexexample.com, and the connector isaccounts.google.com.Dex returns a 302 Redirect to the connector IDP, https://accounts.google.com/o/oauth2/v2/auth?client_id=237800849078-hri2ndt7gdafpf34kq8crd5sik9pe3so.apps.googleusercontent.com&redirect_uri=https%3A%2F%2Fdexexample.com%2Fauth%2Fcallback&response_type=code&scope=openid+email&state=g3dkmpontsr3ugocoddjx72ef. The attacker records the state parameter value g3dkmpontsr3ugocoddjx72ef which will be used as the request ID later on.
The malicious website redirects the victim’s browser to the connector IDP.
The user authenticates to the connector IDP. If they have authenticated before, they may not be presented with an authentication challenge. The user will silently be taken through the following steps:
Authentication with the connector IDP, which redirects the browser to the Dex callback with a code - https://dexexample.com/callback?state=g3dkmpontsr3ugocoddjx72ef&code=4%2F0AX4XfWizg1PQEQNl18hmP0_YQ3iUYII2ed13n9ikKr_ZcV7uCZpZaPcIlxBzX5QwFIcs-w&scope=email+openid+https%3A%2F%[2Fwww.googleapis.com](http://2fwww.googleapis.com/)%2Fauth%2Fuserinfo.email&authuser=0&hd=[google.com](http://google.com/)&prompt=none
Dex handles the callback, fetching the user claims from the connector IDP, persisting them and generating an OAuth code. Then Dex redirects the browser to the approval endpoint https://dexexample.com/approval?req=g3dkmpontsr3ugocoddjx72ef. Note that the req parameter is the same as the attacker's recorded state parameter.
Dex uses the request ID to look up the OAuth code, and builds a redirect to the original callback with the code - http://localhost:40393/auth/callback?code=bz5p3oov2wlh5k3rboa4atxas&state=2AaJAjhpUmsB25csCo5muvorMTl.
In step 2., when the webserver initiates the connection to Dex and receives the redirect to the connector IDP, the webserver will persist the connector state parameter (g3dkmpontsr3ugocoddjx72ef), which is used as the request ID to later look up the OAuth code. As the user goes through the authentication flow with the connector IDP, the webserver will repeatedly request /approval?req=<state>. Once the user has successfully authenticated, if the webserver is able to call /approval before the victim’s browser calls /approval, then an attacker can fetch the Dex OAuth code which can be exchanged for an ID token using the /token endpoint.
Note that PKCE does not defend against this attack since the webserver initiates the request to Dex with a known code challenge.
Fix
The request has been made unpredictable with message authentication. This was accomplished by creating an HMAC using a randomly generated per-request secret. This secret is persisted between the initial login request and the approval request. Since the HMAC is derived using a secret key, its value cannot be known to an attacker, so they will be unable to poll /approval for the code.
Patches
Update to 2.35.0.
Workarounds
No known workarounds (without impacting behavior) for existing versions.
Disabling public clients is the only way to defend against attacks exploiting this vulnerability.
References
For more information
If you have any questions or comments about this advisory:
- Start a new discussion
- Email us at cncf-dex-maintainers@lists.cncf.io
Common Weakness Enumeration (CWE)
Missing Authorization
GitHub
CVSS SCORE
9.3critical| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| github.com/dexidp/dex | golang | - | - | <=2.34.0 | 2.35.0 |
| github.com/dexidp/dex | golang | - | - | <0.0.0-20221003101923-e4bceef9f3d1 | 0.0.0-20221003101923-e4bceef9f3d1 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator.
An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any or all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
There is no impact to availability within the impacted component.
NIST
CVSS SCORE
9.3criticalAlpine
-
Red Hat
2.8
CVSS SCORE
6.5mediumChainguard
CGA-4835-68mx-7g8j
-
Chainguard
CGA-6frp-wh32-6r3c
-
intheWild
-
-