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CVE-2025-59420

7.5 high SSVC exploitation: poc Modified
NVD · CVE.org

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.

Fix

Patch, vendor advisory and mitigation references on NVD 2

Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.

Change history 1

  1. First seenCVSS 7.5 · authlibNVD modified 2026-10-19 16:10

Affected (CPE criteria) 1

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

References 3