PyJWT versions before 2.13.0 contain a vulnerability where PyJWKClient does not restrict URI schemes when fetching keys, passing the URI directly to urllib.request.urlopen(). This allows an attacker who can influence the jku URL to cause Server-Side Request Forgery (SSRF) to local files (file://), FTP, or data URIs. While the library does not directly expose non-HTTP(S) contents to attackers, chained exploitation with additional application flaws could enable token forgery. The issue is addressed in PyJWT 2.13.0.

An attacker able to control the jku URL input to PyJWKClient can cause the library to fetch arbitrary local files or perform SSRF via non-HTTP(S) schemes, potentially leading to information disclosure or token forgery if combined with other application vulnerabilities. The direct impact is limited by the need for attacker influence over jku URLs and additional flaws for full token forgery. No known active exploitation has been reported.

A fix is available in PyJWT version 2.13.0. Users should upgrade to this version or later to address the vulnerability. Since this is a cloud-hosted service, the vendor manages remediation for the cloud environment. Check the vendor advisory for confirmation and further guidance. No additional mitigation is indicated by the vendor advisory.