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CVE-2026-48523 (GCVE-0-2026-48523)
Vulnerability from cvelistv5 – Published: 2026-05-28 15:10 – Updated: 2026-05-28 15:27
VLAI
Title
PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys
Summary
PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0.
Severity
5.4 (Medium)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
- CWE-347 - Improper Verification of Cryptographic Signature
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://github.com/jpadilla/pyjwt/security/adviso… | x_refsource_CONFIRM |
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PYSEC-2026-176
Vulnerability from pysec - Published: 2026-05-28 16:16 - Updated: 2026-06-02 10:34
VLAI
Details
PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0.
Severity
5.4 (Medium)
Impacted products
| Name | purl | pyjwt | pkg:pypi/pyjwt |
|---|
Aliases
{
"affected": [
{
"ecosystem_specific": {},
"package": {
"ecosystem": "PyPI",
"name": "pyjwt",
"purl": "pkg:pypi/pyjwt"
},
"ranges": [
{
"events": [
{
"introduced": "2.9.0"
},
{
"fixed": "2.12.1"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.10.0",
"2.10.1",
"2.11.0",
"2.12.0",
"2.9.0"
]
}
],
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"CVE-2026-48523",
"GHSA-jq35-7prp-9v3f"
],
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"id": "PYSEC-2026-176",
"modified": "2026-06-02T10:34:20.952243Z",
"published": "2026-05-28T16:16:29.280Z",
"references": [
{
"type": "EVIDENCE",
"url": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f"
}
],
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N",
"type": "CVSS_V3"
}
]
}