Vulnerability Description
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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Authlib | Authlib | < 1.6.9 |
Related Weaknesses (CWE)
References
- https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa7Patch
- https://github.com/authlib/authlib/releases/tag/v1.6.9ProductRelease Notes
- https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6jExploitMitigationVendor Advisory
FAQ
What is CVE-2026-28498?
CVE-2026-28498 is a vulnerability with a CVSS score of 7.5 (HIGH). 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 ...
How severe is CVE-2026-28498?
CVE-2026-28498 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-28498?
Check the references section above for vendor advisories and patch information. Affected products include: Authlib Authlib.