{"id":"CVE-2026-48523","aliases":["GHSA-jq35-7prp-9v3f","PYSEC-2026-176"],"url":"https://o3.security/vulnerability/CVE-2026-48523","summary":"PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys","details":"PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0.","published":"2026-05-28T15:10:19.141Z","modified":"2026-08-12T03:51:30.215722235Z","cvss":{"score":5.4,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N"},"epss":{"score":0.00127,"percentile":0.02569,"asOf":"2026-08-25"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"pyjwt","fixedVersion":"2.13.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48523.json"},{"type":"ADVISORY","url":"https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-48523"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:30.215722235Z"}}