VULNERABILITY INTELLIGENCE

CVE-2026-27962

CVSS score9.1 CRITICAL
EPSS probability0.56%
CISA KEVNot currently listed
Published2026-03-16
Last modified2026-09-10
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

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.

Weakness classification

  • security-advisories@github.com: CWE-347
  • 0b0ca135-0b70-47e7-9f44-1890c2a1c46c: CWE-347

Primary references