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MEDIUM

PyJWKClient: missing scheme allowlist enables SSRF + token forgery via file://, ftp://, data: schemes

Published May 28, 2026

Description

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.

Affected products

Remediation

Red Hat statement

This Moderate severity vulnerability in PyJWT's `PyJWKClient` component allows for Server-Side Request Forgery (SSRF) if an application processes attacker-controlled `jku` URLs. While the flaw enables reading local files or broader network access, successful token forging requires additional application-layer vulnerabilities, such as untrusted `jku` derivation or attacker write access to a filesystem path.

Red Hat mitigation

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Metrics

Weaknesses (2)

CWE-441

CWE-918

SSRF

References (8)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner GitHub_M
Published May 28, 2026
Updated Jun 2, 2026
Reserved May 21, 2026
Link CVE-2026-48522
CISA Vulnrichment
Updated Jun 2, 2026
NVD
Status Modified
Modified Jun 17, 2026
Link CVE-2026-48522
Red Hat
Severity Moderate
Public date May 28, 2026
Links CVE-2026-48522 - Bugzilla
GHSA-993G-76C3-P5M4