BREW-MCP-GOOGLE-SHEETS-C… (GHSA-75C5-XW7C-P5PM)

Vulnerability from osv_homebrew – Published: 2026-08-13 17:13 – Updated: 2026-09-10 00:30 – Source website
VLAI
Summary
PyJWT Issuer field partial matches allowed
Details

Summary

The wrong string if check is run for iss checking, resulting in "acb" being accepted for "_abc_".

Details

This is a bug introduced in version 2.10.0: checking the "iss" claim changed from isinstance(issuer, list) to isinstance(issuer, Sequence).

-        if isinstance(issuer, list):
+        if isinstance(issuer, Sequence):
            if payload["iss"] not in issuer:
                raise InvalidIssuerError("Invalid issuer")
        else:

Since str is a Sequnce, but not a list, in is also used for string comparison. This results in if "abc" not in "__abcd__": being checked instead of if "abc" != "__abc__":.

PoC

Check out the unit tests added here: https://github.com/jpadilla/pyjwt-ghsa-75c5-xw7c-p5pm

        issuer = "urn:expected"

        payload = {"iss": "urn:"}

        token = jwt.encode(payload, "secret")

        # decode() succeeds, even though `"urn:" != "urn:expected". No exception is raised.
        with pytest.raises(InvalidIssuerError):
            jwt.decode(token, "secret", issuer=issuer, algorithms=["HS256"])

Impact

I would say the real world impact is not that high, seeing as the signature still has to match. We should still fix it.

Severity
2.2 (Low)
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:N
2.1 (Low)
CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "pyjwt",
        "resource_purl": "pkg:pypi/pyjwt@2.13.0",
        "upstream_fixed_in": "2.10.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "mcp-google-sheets",
        "purl": "pkg:brew/mcp-google-sheets"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.6.3_4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/pyjwt@2.13.0",
        "name": "pyjwt",
        "resource": "pyjwt",
        "strategy": "registry",
        "subject_version": "2.13.0"
      }
    ]
  },
  "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",
  "id": "BREW-mcp-google-sheets-CVE-2024-53861",
  "modified": "2026-09-10T00:30:25Z",
  "published": "2026-08-13T17:13:13Z",
  "references": [
    {
      "type": "WEB",
      "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": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/1570e708672aa9036bc772476beae8bfa48f4131#diff-6893ad4a1c5a36b8af3028db8c8bc3b62418149843fc382faf901eaab008e380R366"
    },
    {
      "type": "WEB",
      "url": "https://github.com/jpadilla/pyjwt/commit/33022c25525c1020869c71ce2a4109e44ae4ced1"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/jpadilla/pyjwt"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "PyJWT Issuer field partial matches allowed",
  "upstream": [
    "GHSA-75c5-xw7c-p5pm",
    "CVE-2024-53861",
    "PYSEC-2026-1814"
  ]
}



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