CVE-2026-28498
Publication date 16 March 2026
Last updated 16 July 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| python-authlib | 26.04 LTS resolute |
Fixed 1.6.7-1ubuntu0.1~esm1
|
| 24.04 LTS noble |
Fixed 1.3.0-1ubuntu0.1~esm2
|
|
| 22.04 LTS jammy |
Fixed 0.15.5-1ubuntu0.1~esm2
|
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CVSS version:
Base score
8.2 · High
Vector: 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
Base score
9.1 · Critical
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
References
Related Ubuntu Security Notices (USN)
- USN-8557-1
- Authlib vulnerabilities
- 16 July 2026