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CVE-2026-28498

Authlib is a Python library which builds OAuth and OpenID Connect servers.

Published Mar 16, 2026 · updated Sep 10, 2026 · authlib authlib

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.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 16, 2026 · NIST NVD

    Detected

    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) cl

  2. Sep 10, 2026 · NIST NVD

    Updated

    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) cl

Affected

  • cpe authlib/authlibversion unspecified

Sources

  • CVE.orgVulnerability recordCVE-2026-28498

    Official CVE identifier

    cve.org
  • NIST NVDVulnerability recordCVE-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

    nvd.nist.gov

References