Vulnerability in Jpadilla Pyjwt
CVE-2026-48523
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (6.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 6th percentile — 6.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.000
Affected products
- Jpadilla Pyjwt — versions >= 2.9.0, < 2.13.0
- Pyjwt Project
Weakness classification (CWE)
References
- github.com/jpadilla/pyjwt/security/advisories/GHSA-jq35-7prp-9v3f (Exploit, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-48523?
- CVE-2026-48523 is a medium-severity vulnerability in Jpadilla Pyjwt, classified under Improper Verification of Cryptographic Signature. CVSS score: 5.4/10. Published 2026-05-28.
- How severe is CVE-2026-48523?
- Medium severity. CVSS v3 base score is 5.4 out of 10.