PyJWT Issuer field partial matches allowed

Open Source Vulnerabilities GHSA-75c5-xw7c-p5pm

### 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](https://github.com/jpadilla/pyjwt/commit/1570e708672aa9036bc772476beae8bfa48f4131#diff-6893ad4a1c5a36b8af3028db8c8bc3b62418149843fc382faf901eaab008e380R366): checking the "iss" claim changed from `isinstance(issuer, list)` to `isinstance(issuer, Sequence)`. ```diff - 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 ```python 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.

Open Source Vulnerabilities PYSEC-2026-1814

### 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](https://github.com/jpadilla/pyjwt/commit/1570e708672aa9036bc772476beae8bfa48f4131#diff-6893ad4a1c5a36b8af3028db8c8bc3b62418149843fc382faf901eaab008e380R366): checking the "iss" claim changed from `isinstance(issuer, list)` to `isinstance(issuer, Sequence)`. ```diff - 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 ```python 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.

Open Source Vulnerabilities CVE-2024-53861

pyjwt is a JSON Web Token implementation in Python. An incorrect string comparison is run for `iss` checking, resulting in `"acb"` being accepted for `"_abc_"`. This is a bug introduced in version 2.10.0: checking the "iss" claim changed from `isinstance(issuer, list)` to `isinstance(issuer, Sequence)`. 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__":`. Signature checks are still present so real world impact is likely limited to denial of service scenarios. This issue has been patched in version 2.10.1. All users are advised to upgrade. There are no known workarounds for this vulnerability.