Description
PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.prepare_key in jwt/algorithms.py is affected because raw-JWK detector does not normalize accepted Unicode byte-order marks before checking for JSON. This occurs when a public JWK is prefixed with a UTF-8 BOM and used in a mixed-algorithm verification path. As a result, public JWK bypasses asymmetric-key detection and becomes the HMAC secret. Consequently, an attacker who knows the public key can forge authenticated tokens. This issue is fixed in version 2.14.0.
Affected products
pyjwt_project: pyjwt
References4
- github.com/jpadilla/pyjwt/security/advisories/GHSA-r6x4-923q-g9… ExploitMitigationVendor Advisory
- github.com/jpadilla/pyjwt/security/advisories/GHSA-r6x4-923q-g9… ExploitMitigationVendor Advisory
- github.com/jpadilla/pyjwt/commit/180783930de91876bc0d601f826a1f… Patch
- github.com/jpadilla/pyjwt/releases/tag/2.14.0 ProductRelease Notes
Metrics
- CVSS 3.1
-
7.4
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS — exploit probability
- 0% percentile: 12 · 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.