SB2025103162 - Incorrect authorization in Authlib
Published: October 31, 2025
Security Bulletin ID
SB2025103162
Severity
High
Patch available
YES
Number of vulnerabilities
1
Exploitation vector
Remote access
Highest impact
Data manipulation
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 1 security vulnerability.
1) Incorrect authorization (CVE-ID: CVE-2025-59420)
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 update from vendor's website.