{"id":"CVE-2024-53861","aliases":["GHSA-75c5-xw7c-p5pm","PYSEC-2026-1814"],"title":"PyJWT Issuer field partial matches allowed","summary":"PyJWT Issuer field partial matches allowed","severity":"low","cvss":2.2,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:N","vendor":"pyjwt","product":"pyjwt","ecosystem":"pip","affected":["pyjwt >= 2.10.0, < 2.10.1"],"patched":["pyjwt 2.10.1"],"published":"2024-12-02","updated":"2026-09-10","sourceUpdated":"2026-09-10T03:50:21.333090692Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-75c5-xw7c-p5pm","references":[{"url":"https://github.com/jpadilla/pyjwt/security/advisories/GHSA-75c5-xw7c-p5pm"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2024-53861"},{"url":"https://github.com/jpadilla/pyjwt/commit/1570e708672aa9036bc772476beae8bfa48f4131#diff-6893ad4a1c5a36b8af3028db8c8bc3b62418149843fc382faf901eaab008e380R366"},{"url":"https://github.com/jpadilla/pyjwt/commit/33022c25525c1020869c71ce2a4109e44ae4ced1"},{"url":"https://github.com/jpadilla/pyjwt"}],"tags":["osv","pip"],"epss":0.00832,"epssPercentile":0.55623,"ingestedAt":"2026-07-08T18:25:46.765Z","slug":"CVE-2024-53861","body":"## Overview\n\n### 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\n\n## Affected packages\n\n- `pyjwt >= 2.10.0, < 2.10.1`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `pyjwt 2.10.1`","depth":"sunlit","depthScore":12,"depthScoreParts":{"impact":12.1,"likelihood":0.2,"exploitation":0,"ransomware":0},"changes":[]}