CVE-2026-41425

There is no CSRF protection on the cache feature on most integrations clients.

Details

In authlib.integrations.starlette_client.OAuth, no CSRF protection is set up when using the cache parameter. When not using the cache parameter, the use of SessionMiddleware ties the client to the auth state, preventing CSRF attacks. With the cache, there is no such mechanism. Other integratons have the same issue, it's not just starlette.

The state parameter is taken from the callback URL and the state is fetched from the cache without checking that it is the same client calling the redirect endpoint as was the one that initiated the auth flow.

This issue is documented in RFC 6749 section 10.12:
https://datatracker.ietf.org/doc/html/rfc6749#section-10.12

PoC

• Set up a Starlette integration with a cache
• The attacker starts the auth flow up until before the callback URL is followed.
• The attacked sends the redirect URL to the victim
• The victim now completes the authorisation

This impacts all users that use the cache to store auth state.

All users will be vulnerable to CSRF attacks and may have an attacker's account tied to their own.

A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones. Typical impact: state-changing actions performed as the victim without their consent.

CVE-2026-41425 has a CVSS score of 5.4 (Medium). 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 (1.6.11); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-41425? CVE-2026-41425 is a medium-severity cross-site request forgery (CSRF) vulnerability in authlib (pip), affecting versions < 1.6.11. It is fixed in 1.6.11. A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones.
2. How severe is CVE-2026-41425? CVE-2026-41425 has a CVSS score of 5.4 (Medium). 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 authlib are affected by CVE-2026-41425? authlib (pip) versions < 1.6.11 is affected.
4. Is there a fix for CVE-2026-41425? Yes. CVE-2026-41425 is fixed in 1.6.11. Upgrade to this version or later.
5. Is CVE-2026-41425 exploitable, and should I be worried? Whether CVE-2026-41425 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-2026-41425 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-2026-41425? Upgrade authlib to 1.6.11 or later.