Bug 2542668 (CVE-2026-101918)

Summary: CVE-2026-101918 pyjwt: PyJWT: Denial of Service via deeply nested JSON token payload
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in PyJWT. When processing a JSON Web Token (JWT) prior to signature verification, the parser fails to properly handle deeply nested data, leading to an unhandled recursion error. A remote unauthenticated attacker could exploit this flaw by submitting a specially crafted token, causing the application to raise an unexpected server exception and resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-09-28 20:31:23 UTC 
PyJWT is a Python implementation of JSON Web Token standards. From 2.0.0a1 until 2.15.0, PyJWT PyJWKClient.get_signing_key_from_jwt is affected because payload parser catches ValueError but not RecursionError. This occurs when an attacker-controlled recursively nested payload reaches json.loads. As a result, documented PyJWT exception handling does not contain the failure. Consequently, an unauthenticated request can raise an exception that may produce an HTTP 500 response. The advisory-defined affected implementation also includes jwt/api_jwt.py, verify_signature=False. This issue is fixed in version 2.15.0.