## Authlib Python Library Exposes Critical JWT Authentication Bypass via JWK Header Injection (CVE-2026-27962)
A critical vulnerability in the widely-used Python authentication library Authlib allows attackers to forge cryptographically valid JWT tokens, completely bypassing server authentication and authorization. The flaw, tracked as CVE-2026-27962, resides in the library's JWS (JSON Web Signature) implementation. When `key=None` is passed to a deserialization function, the library automatically extracts and uses the cryptographic key from the JWT's `jwk` header field—a field that is under the attacker's direct control. This design flaw enables an unauthenticated attacker to 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 valid.

The vulnerability affects all versions of Authlib prior to 1.6.9. Authlib is a foundational library for building OAuth 2.0 and OpenID Connect servers in Python, making this a high-impact security issue for any application relying on it for user authentication and API security. The flaw was identified by the Trivy security scanner in a CI/CD workflow, highlighting its potential for automated discovery in development pipelines. The core failure is a trust violation: the library incorrectly trusts user-supplied header data to provide the key for signature verification, instead of relying on a pre-shared or securely configured server key.

Successful exploitation grants an attacker the same privileges as a legitimately authenticated user, potentially leading to full account takeover, unauthorized data access, and privilege escalation within affected systems. The maintainers have released version 1.6.9 with a patch. All development and security teams using Authlib must immediately upgrade to the patched version. This incident underscores the severe risks in cryptographic library implementations and the critical importance of rigorous security testing in DevSecOps pipelines, especially for authentication components.
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- **Source**: GitHub Issues
- **Sector**: The Lab
- **Tags**: CVE-2026-27962, Python, JWT, Authentication Bypass, DevSecOps
- **Credibility**: unverified
- **Published**: 2026-04-14 14:22:57
- **ID**: 63922
- **URL**: https://whisperx.ai/en/intel/63922