PyJWT is a JSON Web Token implementation in Python. Prior to 2.13.0, PyJWKClient passes its uri argument directly to urllib.request.urlopen() which uses Python stdlib's default OpenerDirector registering HTTPHandler, HTTPSHandler, FTPHandler, FileHandler, and DataHandler. There is currently no documented option to restrict which schemes PyJWKClient will fetch. If an application's jku URL ingestion path accepts attacker-influenced URLs (e.g., from JWT header, configuration file, OAuth flow parameter), the attacker can cause PyJWKClient to read arbitrary local files via file:// (SSRF on local filesystem), cause PyJWKClient to attempt FTP / data-URI fetches (broader SSRF surface), or forge tokens that PyJWT verifies as valid. The library does not directly return non-HTTP(S) URI contents to the attacker; the chained "plant a JWKS to forge tokens" scenario described in the original report requires additional application-layer flaws (attacker write access to a filesystem path, untrusted jku derivation) that this fix does not address. This vulnerability is fixed in 2.13.0.
Fix
Patch, vendor advisory and mitigation references on NVD 2
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-993g-76c3-p5m4 Exploit, Mitigation, Vendor Advisory
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-993g-76c3-p5m4 Exploit, Mitigation, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 4.2 · pyjwt_projectNVD modified 2026-10-26 13:10
Affected (CPE criteria) 1
cpe:2.3:a:pyjwt_project:pyjwt:*:*:*:*:*:*:*:*
References 2
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-993g-76c3-p5m4 Exploit, Mitigation, Vendor Advisory
- https://github.com/jpadilla/pyjwt/security/advisories/GHSA-993g-76c3-p5m4 Exploit, Mitigation, Vendor Advisory