PyJWT: HS256/384/512 verify accepts empty HMAC key via oct JWK (PyJWK/PyJWKClient) enabling token forgery

影響: pip:pyjwt <= 2.13.0 → 2.14.0

HMACAlgorithm.from_jwk accepts a symmetric (kty=oct) JWK whose k value is the empty string and returns a zero-length key without raising. When a token is then verified with that key object (a PyJWK, or a PyJWK resolved by PyJWKSet / PyJWKClient), the HMAC verifier computes HMAC(key=b"", signing_input) and accepts any token an attacker forged with the same empty key. The attacker needs no secret knowledge: they reproduce the digest locally with an empty key and set the token's kid to the empty-k…

Read on GitHub Advisory Database

On 10/23/2026, 12:48 AM, GitHub Advisory Database published "PyJWT: HS256/384/512 verify accepts empty HMAC key via oct JWK (PyJWK/PyJWKClient) enabling token forgery" (type: Advisory). Severity is "High" (high). Related technologies: Python.