cvedb.io
CVE-2026-27962
CRITICAL · CVSS 9.1
EPSS exploitation probability: 0%
Published 2026-03-16T18:16:07.383 · Last modified 2026-07-01T13:16:55.487

Summary

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.

Affected products

authlib — authlib

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References

This product uses data from the NVD API but is not endorsed or certified by the NVD. Informational only; not professional security advice.