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.
- CVSS 3.1
- 5.4
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N - EPSS
- 0.1% chance of exploitation in the next 30 days; higher than 2% of CVEs (scores of 2026-10-25)
- CWE
- CWE-347
- Published
- Modified
- Record from
- the NVD, synced
Affected
- pyjwt_project:pyjwt
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-jq35-7prp-9v3f | PyPI | pyjwt | >=2.9.0 <2.13.0 | 2.13.0 |
| PYSEC-2026-176 | PyPI | pyjwt | >=2.9.0 <2.12.1 | 2.12.1 |