CVE-2026-28498

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter. The library intercepts the unsupported state and silently returns True (validation passed), inherently violating fundamental cryptographic design principles and direct OIDC specifications. This issue has been patched in version 1.6.9.
Configurations

Configuration 1 (hide)

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

History

17 Mar 2026, 20:40

Type Values Removed Values Added
CVSS v2 : unknown
v3 : unknown
v2 : unknown
v3 : 7.5
References () https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa72b - () https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa72b - Patch
References () https://github.com/authlib/authlib/releases/tag/v1.6.9 - () https://github.com/authlib/authlib/releases/tag/v1.6.9 - Product, Release Notes
References () https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6j - () https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6j - Exploit, Mitigation, Vendor Advisory
CPE cpe:2.3:a:authlib:authlib:*:*:*:*:*:*:*:*
First Time Authlib authlib
Authlib

16 Mar 2026, 18:16

Type Values Removed Values Added
New CVE

Information

Published : 2026-03-16 18:16

Updated : 2026-03-17 20:40


NVD link : CVE-2026-28498

Mitre link : CVE-2026-28498

CVE.ORG link : CVE-2026-28498


JSON object : View

Products Affected

authlib

  • authlib
CWE
CWE-354

Improper Validation of Integrity Check Value

CWE-573

Improper Following of Specification by Caller