Vulnerability · Published May 28, 2026 · Assigned by GitHub_M
CVE-2026-48523PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys
Medium 5.4
In plain English
A medium-severity security flaw in pyjwt from jpadilla. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 2% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | pyjwt | no fix listed | DEBIAN-CVE-2026-48523 |
| Debian:14 | pyjwt | 2.13.0-1 | DEBIAN-CVE-2026-48523 |
| PyPI | pyjwt | 2.12.1 | PYSEC-2026-176 |
| PyPI | pyjwt | 2.13.0 | GHSA-jq35-7prp-9v3f |
| Ubuntu:22.04:LTS | pyjwt | 2.3.0-1ubuntu0.4 | USN-8823-1 |
| Ubuntu:24.04:LTS | pyjwt | 2.7.0-1ubuntu0.2 | USN-8823-1 |
| Ubuntu:25.10 | pyjwt | no fix listed | UBUNTU-CVE-2026-48523 |
| Ubuntu:26.04:LTS | pyjwt | 2.10.1-4ubuntu1.1 | USN-8823-1 |
| Ubuntu:26.04:LTS | pyjwt | 2.10.1-4ubuntu1.1 | UBUNTU-CVE-2026-48523 |
Affected products (as reported)
Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
References
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f x_refsource_CONFIRM