CVE-2026-27962

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 Software

VendorProductVersion RangeStatus
authlibauthlib< 1.6.9affected

Weaknesses

  • CWE-347: CWE-347: Improper Verification of Cryptographic Signature

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: poc
    • Automatable: yes
    • Technical Impact: total

authlib: Authlib: Authentication bypass due to JWK Header Injection vulnerability

Additional References

References