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.

A flaw was found in Authlib, a Python library used for creating secure authentication and authorization systems. This vulnerability, known as JWK (JSON Web Key) Header Injection, affects how Authlib verifies digital signatures in JWS (JSON Web Signature) tokens. An attacker can exploit this by creating a specially crafted token that includes their own cryptographic key in the header. When the system attempts to verify this token without a predefined key, it mistakenly uses the attacker's key, allowing them to bypass authentication and gain unauthorized access.

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.

Authlib is a Python library which builds OAuth and OpenID Connect serv ...

Authlib JWS JWK Header Injection: Signature Verification Bypass