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.
When the value key=None is passed to any JWS deserialization function, the library extracts the cryptographic key directly from the attacker-controlled 'jwk' header field of the JWT. The attacker signs the token with their own private key and embeds the matching public key in the token header. The server accepts such a crafted token as cryptographically valid, even though the key comes from the attacker rather than a trusted source. This way it is possible to forge the identity of any user or obtain unauthorized privileges.
An attacker can completely bypass authentication and authorization by impersonating any user or gaining unauthorized access to protected application resources.
Update Authlib to version 1.6.9 or newer. Patch available in the official GitHub project repository (tag v1.6.9).
Authlib (Python library) in versions earlier than 1.6.9
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NAuthlib
APPAuthlib< 1.6.9
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