PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys_CVE-2026-48523

{
    "lastseen": "",
    "description": "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.",
    "published": "2026-05-28T15:10:19.141Z",
    "modified": "2026-05-28T15:27:49.780Z",
    "type": "cve",
    "title": "PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys",
    "source": "GitHub_M",
    "references": "https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f",
    "id": "CVE-2026-48523",
    "bulletinFamily": "",
    "cwe": [
        "CWE-347"
    ],
    "cvelist": null,
    "sourceData": "jpadilla pyjwt >= 2.9.0, < 2.13.0",
    "sourceHref": "",
    "cvss": {
        "score": 5.4,
        "severity": "MEDIUM",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
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            "privilegesRequired": "",
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            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "pyjwt",
    "version": ">= 2.9.0, < 2.13.0",
    "vendor": "jpadilla",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
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    "ai_score": 0
}