#VU124064 Improper validation of integrity check value in authlib - CVE-2026-28498
Published: March 17, 2026
Vulnerability identifier: #VU124064
Vulnerability risk: High
CVSSv4.0: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-28498
CWE-ID: CWE-354
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 authentication checks.
The vulnerability exists due to an error in internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims, which exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. A remote attacker can bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter and bypass validation of OpenID Connect (OIDC) ID Tokens.
Remediation
Install updates from vendor's website.