joserfc claim-validation bypass via array-typed single-string claims (iss/sub/jti)

{
  "id": "2c087d7fa599da88efae2c150a8e8bd84ac13e3db7688f4260c2b602a4a0512b",
  "url": "https://osv.dev/vulnerability/CVE-2026-75509",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "joserfc claim-validation bypass via array-typed single-string claims (iss/sub/jti)",
    "summary": "joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to version 1.7.3, JWTClaimsRegistry applies membership matching to list-valued iss and sub claims, allowing an array-valued iss that contains the expected issuer to pass an intended equality check and enabling issuer-validation bypass. This issue is fixed in version 1.7.3.",
    "evidence": "osv:CVE-2026-75509",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-75509",
      "aliases": [
        "CVE-2026-75509",
        "GHSA-r74j-q665-7rpj"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/authlib/joserfc",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "64264890f4f7d414c970681be55b47e28dd50e4b"
                },
                {
                  "fixed": "76ee6a59bf5773c0af00b99076c5e199031f97f1"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "1.7.3"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "76ee6a59bf5773c0af00b99076c5e199031f97f1"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "1.7.2",
            "1.7.1",
            "1.7.0",
            "1.6.7",
            "1.6.5",
            "1.6.4",
            "1.6.3",
            "1.6.2",
            "1.6.1",
            "1.6.0",
            "1.5.0",
            "1.4.3",
            "1.4.1",
            "1.4.0",
            "1.3.3",
            "1.3.2",
            "1.3.1",
            "1.3.0",
            "1.2.2",
            "1.2.1",
            "1.2.0",
            "1.1.0",
            "1.0.4",
            "1.0.3",
            "1.0.2",
            "1.0.1",
            "1.0.0",
            "0.12.0",
            "0.11.1",
            "0.11.0",
            "0.10.0",
            "0.9.0",
            "0.8.0",
            "0.7.0",
            "0.6.0",
            "0.5.0",
            "0.4.0",
            "0.3.0",
            "0.2.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-75509.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:45.614825618Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/75xxx/CVE-2026-75509.json",
        "https://github.com/authlib/joserfc/security/advisories/GHSA-r74j-q665-7rpj",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-75509",
        "https://github.com/authlib/joserfc/commit/76ee6a59bf5773c0af00b99076c5e199031f97f1"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-290",
          "CWE-345"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/75xxx/CVE-2026-75509.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-75509",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 513690,
  "published_at": "2026-08-24T20:08:07.088+00:00"
}