#VU117879 Incorrect authorization in authlib - CVE-2025-59420
Published: October 31, 2025
Vulnerability identifier: #VU117879
Vulnerability risk: High
CVSSv4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2025-59420
CWE-ID: CWE-863
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerable software:
authlib
authlib
Software vendor:
Authlib
Authlib
Description
The vulnerability allows a remote attacker to bypass authorization checks.
The vulnerability exists due to 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.
Remediation
Install updates from vendor's website.