{"id":"CVE-2026-102266","state":"PUBLISHED","title":"PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation","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.","publishedAt":"2026-09-28T20:21:26.164Z","updatedAt":"2026-09-29T19:35:42.049Z","severity":{"score":7.4,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["jpadilla pyjwt"],"affected":[{"vendor":"jpadilla","product":"pyjwt","versions":[{"version":">= 2.13.0, < 2.14.0","status":"affected"}]}],"references":["https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r","https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c","https://github.com/jpadilla/pyjwt/releases/tag/2.14.0"],"weaknesses":["CWE-347"],"ingestedAt":"2026-10-29T20:10:13.529Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/102xxx/CVE-2026-102266.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-102266","state":"PUBLISHED","datePublished":"2026-09-28T20:21:26.164Z","dateUpdated":"2026-09-29T19:35:42.049Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-09-28T20:11:16.658Z"},"containers":{"cna":{"title":"PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"jpadilla","product":"pyjwt","versions":[{"version":">= 2.13.0, < 2.14.0","status":"affected"}]}],"references":[{"url":"https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r","name":"https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c","name":"https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c","tags":["x_refsource_MISC"]},{"url":"https://github.com/jpadilla/pyjwt/releases/tag/2.14.0","name":"https://github.com/jpadilla/pyjwt/releases/tag/2.14.0","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":7.4,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-347","lang":"en","description":"CWE-347: Improper Verification of Cryptographic Signature","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-09-28T20:21:26.164Z"},"source":{"advisory":"GHSA-9j54-fg26-wv3r","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-29T19:28:36.086597Z","id":"CVE-2026-102266","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-29T19:35:42.049Z"}}]}}}