CVE-2024-23647

PKCE is a very important countermeasure in OAuth2 , both for public and confidential clients. It protects against CSRF attacks and code injection attacks. Because of this bug, an attacker can circumvent the protection PKCE offers.

Details

There is a bug in our implementation of PKCE that allows an attacker to circumvent the protection that PKCE offers. PKCE adds the code_challenge’ parameter to the authorization request and adds the code_verifier’ parameter to the token request. We recently fixed a downgrade attack (in v2023.8.5 and 2023.10.4) where if the attacker removed the code_verifier’ parameter in the token request, authentik would allow the request to pass, thus circumventing PKCE’s protection. However, in the latest version of the software, another downgrade scenario is still possible: if the attacker removes the code_challenge’ parameter from the authorization request, authentik will also not do the PKCE check.

Note that this type of downgrade enables an attacker to perform a code injection attack, even if the OAuth client is using PKCE (which is supposed to protect against code injection attacks). To start the attack, the attacker must initiate the authorization process without that code_challenge’ parameter in the authorization request. But this is easy to do (just use a phishing site or email to trick the user into clicking on a link that the attacker controls, the authorization link without that code_challenge’ parameter).

The OAuth BCP (https://datatracker.ietf.org/doc/html/draft-ietf-oauth-security-topics) explicitly mentions this particular attack in section 2.1.1: “Authorization servers MUST mitigate PKCE Downgrade Attacks by ensuring that a token request containing a code_verifier parameter is accepted only if a code_challenge parameter was present in the authorization request, see Section 4.8.2 for details.”

For more information

If you have any questions or comments about this advisory:

• Email us at [email protected]

The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.

CVE-2024-23647 has a CVSS score of 6.5 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2023.10.7, 2023.8.7); upgrading removes the vulnerable code path.

Kodem intelligence

authentik 2023.8.7 and 2023.10.7 fix this issue.

1. What is CVE-2024-23647? CVE-2024-23647 is a high-severity improper authentication vulnerability in goauthentik.io (go), affecting versions >= 2023.10.0, <= 2023.10.6. It is fixed in 2023.10.7, 2023.8.7. The application does not adequately verify the identity of a user, device, or process before granting access.
2. How severe is CVE-2024-23647? CVE-2024-23647 has a CVSS score of 6.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of goauthentik.io are affected by CVE-2024-23647? goauthentik.io (go) versions >= 2023.10.0, <= 2023.10.6 is affected.
4. Is there a fix for CVE-2024-23647? Yes. CVE-2024-23647 is fixed in 2023.10.7, 2023.8.7. Upgrade to this version or later.
5. Is CVE-2024-23647 exploitable, and should I be worried? Whether CVE-2024-23647 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2024-23647 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2024-23647?
   • Upgrade goauthentik.io to 2023.10.7 or later
   • Upgrade goauthentik.io to 2023.8.7 or later