CVE-2026-120459 PUBLISHED

python-jose through 3.5.0 contains an authentication bypass vulnerability that allows unauthenticated attackers to forge JWTs because HMACKey and CryptographyHMACKey accept zero-length HMAC secrets. When an application's HS256/HS384/HS512 verification key resolves to empty, such as an oct JWK with empty k, attackers can forge tokens with arbitrary claims that jwt.decode accepts.

• Gavin Blacklock finder
• Conner Webber finder

• https://github.com/mpdavis/python-jose/issues/398
• https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/native.py
• https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/cryptography_backend.py
• VulnCheck Advisory: python-jose through 3.5.0 Authentication Bypass via Empty HMAC Key

• Improper Verification of Cryptographic Signature CWE