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 CVE-2026-48523

To remediate CVE-2026-48523, upgrade the affected package to a fixed version below.

• —no fix listed
• —upgrade to 2.12.1 or later

Is CVE-2026-48523 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0
• >= 2.9.0, < 2.12.1

CVSS scores

References (2)

• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-48523
• EXPLOITgithub.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f