CVE-2025-59420

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.4, Authlib’s JWS verification accepts tokens that declare unknown critical header parameters (crit), violating RFC 7515 “must‑understand” semantics. An attacker can craft a signed token with a critical header (for example, bork or cnf) that strict verifiers reject but Authlib accepts. In mixed‑language fleets, this enables split‑brain verification and can lead to policy bypass, replay, or privilege escalation. This issue has been patched in version 1.6.4.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/authlib/authlib/commit/6b1813e4392eb7c168c276099ff7783b176479df	Patch
https://github.com/authlib/authlib/security/advisories/GHSA-9ggr-2464-2j32	Exploit Vendor Advisory
https://lists.debian.org/debian-lts-announce/2025/10/msg00032.html

Configurations

Configuration 1 (hide)

cpe:2.3:a:authlib:authlib:*:*:*:*:*:*:*:*

History

19 Oct 2026, 16:10

Type	Values Removed	Values Added
Summary		(es) Authlib es una biblioteca de Python que construye servidores OAuth y OpenID Connect. Antes de la versión 1.6.4, la verificación JWS de Authlib acepta tokens que declaran parámetros de encabezado críticos (crit) desconocidos, violando la semántica de 'must-understand' de RFC 7515. Un atacante puede crear un token firmado con un encabezado crítico (por ejemplo, bork o cnf) que los verificadores estrictos rechazan pero Authlib acepta. En flotas de lenguaje mixto, esto permite la verificación de cerebro dividido y puede conducir a la omisión de políticas, la repetición o la escalada de privilegios. Este problema ha sido parcheado en la versión 1.6.4.

Information

Published : 2025-09-22 18:15

Updated : 2026-10-19 16:10

NVD link : CVE-2025-59420

Mitre link : CVE-2025-59420

CVE.ORG link : CVE-2025-59420

JSON object : View

Products Affected

authlib

authlib

CWE

CWE-345

Insufficient Verification of Data Authenticity

CWE-863

Incorrect Authorization

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