CVE-2026-102266

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.from_jwk is affected because PyJWK verification path used the decoded key without applying prepare_key validation. This occurs when a trusted JWK Set contains an oct entry with an empty k value. As a result, an attacker signs an HMAC token with the same zero-length key accepted by PyJWT. Consequently, forged token can carry arbitrary authenticated claims. This issue is fixed in version 2.14.0.

• CWE-347

• https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934cPatch
• https://github.com/jpadilla/pyjwt/releases/tag/2.14.0Product, Release Notes
• https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3rExploit, Vendor Advisory
• https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3rExploit, Vendor Advisory

Published

Sep 28, 2026

Last Modified

Oct 7, 2026

Status

Analyzed

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