Vulnerability Description
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header Injection vulnerability in authlib's JWS implementation allows an unauthenticated attacker to forge arbitrary JWT tokens that pass signature verification. When key=None is passed to any JWS deserialization function, the library extracts and uses the cryptographic key embedded in the attacker-controlled JWT jwk header field. An attacker can sign a token with their own private key, embed the matching public key in the header, and have the server accept the forged token as cryptographically valid — bypassing authentication and authorization entirely. This issue has been patched in version 1.6.9.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Authlib | Authlib | < 1.6.9 |
Related Weaknesses (CWE)
References
- https://github.com/authlib/authlib/commit/a5d4b2d4c9e46bfa11c82f85fdc2bcc0b50ae6Patch
- https://github.com/authlib/authlib/releases/tag/v1.6.9ProductRelease Notes
- https://github.com/authlib/authlib/security/advisories/GHSA-wvwj-cvrp-7pv5ExploitMitigationVendor Advisory
FAQ
What is CVE-2026-27962?
CVE-2026-27962 is a vulnerability with a CVSS score of 9.1 (CRITICAL). Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header Injection vulnerability in authlib's JWS implementation allows an unauthenticated attack...
How severe is CVE-2026-27962?
CVE-2026-27962 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-27962?
Check the references section above for vendor advisories and patch information. Affected products include: Authlib Authlib.