Vulnerability 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Pyjwt Project | Pyjwt | >= 2.9.0, < 2.12.1 |
Related Weaknesses (CWE)
References
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3fExploitVendor Advisory
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3fExploitVendor Advisory
FAQ
What is CVE-2026-48523?
CVE-2026-48523 is a vulnerability with a CVSS score of 5.4 (MEDIUM). 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. T...
How severe is CVE-2026-48523?
CVE-2026-48523 has been rated MEDIUM with a CVSS base score of 5.4/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-48523?
Check the references section above for vendor advisories and patch information. Affected products include: Pyjwt Project Pyjwt.