PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys

{
  "id": "41f13e2f62647503d080ebcb2acf0f0f3cd6199b1f96964ddad24df6fead06f4",
  "url": "https://osv.dev/vulnerability/CVE-2026-48523",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys",
    "summary": "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.",
    "evidence": "osv:CVE-2026-48523",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-48523",
      "aliases": [
        "CVE-2026-48523",
        "GHSA-jq35-7prp-9v3f",
        "PYSEC-2026-176"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/jpadilla/pyjwt",
              "type": "GIT",
              "events": [
                {
                  "introduced": "868cf4ab2ca5a0a39da40e5a14dd740b203662b2"
                },
                {
                  "fixed": "7144e4534c34810f4525dc4578a32addd8212cff"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "2.9.0"
                      },
                      {
                        "fixed": "2.13.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "cpe": "cpe:2.3:a:pyjwt_project:pyjwt:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "2.9.0"
                      },
                      {
                        "fixed": "2.13.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2.12.1",
            "2.12.0",
            "2.11.0",
            "2.10.1",
            "2.10.0",
            "2.9.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-48523.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:33.979697082Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48523.json",
        "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-48523"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-347"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48523.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-48523",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 501170,
  "published_at": "2026-05-28T15:10:19.141+00:00"
}