Description
PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, is_pem_format in jwt/utils.py is affected because is_pem_format does not recognize every PEM representation accepted by the cryptography loader. This occurs when an application mixes HMAC and asymmetric algorithms and supplies a mutated public-key PEM as raw key bytes. As a result, HMACAlgorithm.prepare_key treats the unrecognized asymmetric public key as an HMAC secret. Consequently, an attacker who knows the public key can forge authenticated HMAC tokens. This issue is fixed in version 2.14.0.
Affected products
pyjwt_project: pyjwt
References4
- github.com/jpadilla/pyjwt/security/advisories/GHSA-ffc3-869f-jx… ExploitVendor Advisory
- github.com/jpadilla/pyjwt/security/advisories/GHSA-ffc3-869f-jx… ExploitVendor Advisory
- github.com/jpadilla/pyjwt/commit/8b4e233a22206b34ec1186e912e75c… Patch
- github.com/jpadilla/pyjwt/releases/tag/2.14.0 ProductRelease Notes
Metrics
- CVSS 3.1
-
9.1
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS — exploit probability
- 0% percentile: 15 · as of 9 November 2026
- CWE
- CWE-347
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.