{"id":"CVE-2024-53861","aliases":["GHSA-75c5-xw7c-p5pm","PYSEC-2026-1814"],"url":"https://o3.security/vulnerability/CVE-2024-53861","summary":"Issuer field partial matches allowed in pyjwt","details":"### Summary\nThe wrong string if check is run for `iss` checking, resulting in `\"acb\"` being accepted for `\"_abc_\"`.\n\n### Details\nThis is a bug introduced in version [2.10.0](https://github.com/jpadilla/pyjwt/commit/1570e708672aa9036bc772476beae8bfa48f4131#diff-6893ad4a1c5a36b8af3028db8c8bc3b62418149843fc382faf901eaab008e380R366): checking the \"iss\" claim\nchanged from `isinstance(issuer, list)` to `isinstance(issuer,\nSequence)`.\n\n```diff\n-        if isinstance(issuer, list):\n+        if isinstance(issuer, Sequence):\n            if payload[\"iss\"] not in issuer:\n                raise InvalidIssuerError(\"Invalid issuer\")\n        else:\n```\n\nSince str is a Sequnce, but not a list, `in` is also used for string\ncomparison. This results in `if \"abc\" not in \"__abcd__\":` being\nchecked instead of `if \"abc\" != \"__abc__\":`.\n### PoC\nCheck out the unit tests added here: https://github.com/jpadilla/pyjwt-ghsa-75c5-xw7c-p5pm\n```python\n        issuer = \"urn:expected\"\n\n        payload = {\"iss\": \"urn:\"}\n\n        token = jwt.encode(payload, \"secret\")\n\n        # decode() succeeds, even though `\"urn:\" != \"urn:expected\". No exception is raised.\n        with pytest.raises(InvalidIssuerError):\n            jwt.decode(token, \"secret\", issuer=issuer, algorithms=[\"HS256\"])\n```\n\n\n### Impact\n\nI would say the real world impact is not that high, seeing as the signature still has to match. We should still fix it.\n","published":"2024-11-29T18:43:07.644Z","modified":"2026-08-12T03:51:21.884447572Z","cvss":{"score":2.2,"severity":"LOW","vector":"CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"pyjwt","fixedVersion":"2.10.1"}],"fix":{"url":"https://github.com/jpadilla/pyjwt/commit/1570e708672aa9036bc772476beae8bfa48f4131#diff-6893ad4a1c5a36b8af3028db8c8bc3b62418149843fc382faf901eaab008e380R366","label":"jpadilla/pyjwt@1570e70"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/53xxx/CVE-2024-53861.json"},{"type":"ADVISORY","url":"https://github.com/jpadilla/pyjwt/security/advisories/GHSA-75c5-xw7c-p5pm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-53861"},{"type":"FIX","url":"https://github.com/jpadilla/pyjwt/commit/1570e708672aa9036bc772476beae8bfa48f4131#diff-6893ad4a1c5a36b8af3028db8c8bc3b62418149843fc382faf901eaab008e380R366"},{"type":"FIX","url":"https://github.com/jpadilla/pyjwt/commit/33022c25525c1020869c71ce2a4109e44ae4ced1"},{"type":"PACKAGE","url":"https://github.com/jpadilla/pyjwt"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:21.884447572Z"}}