Authlib up to 1.6.8 Header Parameter integrity check

Summaryinfo

A vulnerability has been found in Authlib up to 1.6.8 and classified as problematic. This impacts an unknown function of the component Header Parameter Handler. The manipulation leads to integrity check. This vulnerability is referenced as CVE-2026-28498. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Authlib up to 1.6.8. It has been rated as problematic. This issue affects an unknown part of the component Header Parameter Handler. The manipulation with an unknown input leads to a integrity check vulnerability. Using CWE to declare the problem leads to CWE-354. The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission. Impacted is integrity. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-28498 since 02/27/2026. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available.

The vulnerability scanner Nessus provides a plugin with the ID 302537 (Linux Distros Unpatched Vulnerability : CVE-2026-28498), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 1.6.9 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (302537) and CERT Bund (WID-SEC-2026-0935). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Red Hat Ansible Automation Platform
• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Fedora Linux
• SUSE Linux
• Oracle Linux
• RESF Rocky Linux
• HCL BigFix
• IBM DB2
• IBM App Connect Enterprise
• Red Hat OpenShift

Productinfo

Name

• Authlib

Version

• 1.6.0
• 1.6.1
• 1.6.2
• 1.6.3
• 1.6.4
• 1.6.5
• 1.6.6
• 1.6.7
• 1.6.8

Website

• Product: https://github.com/authlib/authlib/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion