CVE-2026-48523
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.
How to fix
- pyjwt_project pyjwt2.13.0 or later
- pyjwt2.13.0, 2.12.1 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| pyjwt_project pyjwt | 2.9.0 ≤ v < 2.13.0 | 2.13.0 |
| pyjwtPyPI | 2.9.0 ≤ v < 2.13.0, 2.9.0 ≤ v < 2.12.1 | 2.13.0, 2.12.1 |
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