CVE-2026-27962 - Vulnerability Analysis

Overview

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.

Severity & Score

References

• https://github.com/authlib/authlib/commit/a5d4b2d4c9e46bfa11c82f85fdc2bcc0b50ae681
• https://github.com/authlib/authlib/releases/tag/v1.6.9
• https://github.com/authlib/authlib/security/advisories/GHSA-wvwj-cvrp-7pv5

Related Resources

• Vulnerability Intelligence Dashboard
• Credential Scanner