{"id":"CVE-2026-102266","summary":"PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation","details":"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.","aliases":["GHSA-9j54-fg26-wv3r"],"modified":"2026-09-30T11:30:38.666964424Z","published":"2026-09-28T20:21:26.164Z","database_specific":{"cwe_ids":["CWE-347"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/102xxx/CVE-2026-102266.json","cna_assigner":"GitHub_M"},"references":[{"type":"WEB","url":"https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/102xxx/CVE-2026-102266.json"},{"type":"ADVISORY","url":"https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-102266"},{"type":"FIX","url":"https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/jpadilla/pyjwt","events":[{"introduced":"7144e4534c34810f4525dc4578a32addd8212cff"},{"fixed":"f91ed44dd65baaf457f4b3353ed35e98a753934c"},{"fixed":"c6fe464b356ff4b1ebc9ba62172d331a40aa27df"}],"database_specific":{"source":["AFFECTED_FIELD","REFERENCES"],"extracted_events":[{"introduced":"2.13.0"},{"fixed":"2.14.0"}]}}],"versions":["2.13.0"],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-102266.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"}]}