PyJWT: PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation

[ Why it matters ]Priority signals

• Public proof-of-concept exploit exists (CISA SSVC)
• Critical severity: CVSS 9.1

[ Description ]Official description

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.

[ Fixes ]Fixes and patches

• PyJWT 2.14.0Fixed version · GitHub Advisories · pip package PyJWT: upgrade to 2.14.0 or later (affected >= 2.13.0, < 2.14.0)
• Patch on github.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD

[ Advisories ]Government CERT advisories

• BSI CERT-Bund21 Oct 2026WID-SEC-2026-4111

  Red Hat Ansible Automation Platform: Multiple vulnerabilities Translated from German

  Risk highCVE-2026-11332CVE-2026-102938CVE-2026-103262+21 more CVEs
• CERT-FR2 Oct 2026CERTFR-2026-AVI-1249

  Multiple vulnerabilities in VMware products Translated from French

  Multiple vulnerabilities have been discovered in VMware products. They allow an attacker to cause a security problem not specified by the vendor.

  CVE-2026-75595CVE-2026-53910CVE-2026-56404+288 more CVEs

[ Packages ]Affected open-source packages

• PyJWT pipAffected >= 2.13.0, < 2.14.0 · fixed in 2.14.0 · GHSA-9j54-fg26-wv3r

[ References ]References

• github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934cPatch
• github.com/jpadilla/pyjwt/releases/tag/2.14.0ProductRelease Notes
• github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3rExploitVendor Advisory