Vulnerability Details CVE-2026-48523
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 2.6%
CVSS Severity
CVSS v3 Score 5.4
References
Products affected by CVE-2026-48523
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cpe:2.3:a:pyjwt_project:pyjwt:2.10.0
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cpe:2.3:a:pyjwt_project:pyjwt:2.10.1
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cpe:2.3:a:pyjwt_project:pyjwt:2.11.0
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cpe:2.3:a:pyjwt_project:pyjwt:2.12.0
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cpe:2.3:a:pyjwt_project:pyjwt:2.9.0