23 Oct 2026 15:48:27 UTC
Authlib JWS JWK Header Injection: Signature Verification Bypass
cve-program · CVE-2026-27962 · Published
CVE-2026-27962
Authlib JWS JWK Header Injection: Signature Verification Bypass
CVSS 3.1 9.1 CRITICALCheck source for fixed versionsKEV status unknown
cve-program · CVE-2026-27962
PublishedAuthlib 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.
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