PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys

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.

Problem type

CWE-347: Improper Verification of Cryptographic Signature

Affected products

jpadilla

pyjwt

>= 2.9.0, < 2.13.0 - AFFECTED

References

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f

https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f

x_refsource_CONFIRM

JSON source

https://cveawg.mitre.org/api/cve/CVE-2026-48523

Click to expand

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