---
id: CVE-2026-28498
title: Authlib is a Python library which builds OAuth and OpenID Connect servers
summary: >-
  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. S…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'
cwe:
  - CWE-354
  - CWE-573
  - CWE-325
vendor: authlib
product: authlib
affected:
  - authlib < 1.6.9
patched:
  - authlib 1.6.9
published: '2026-03-16'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T13:18:01.797'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-28498'
references:
  - url: >-
      https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa72b
    label: security-advisories@github.com
  - url: 'https://github.com/authlib/authlib/releases/tag/v1.6.9'
    label: security-advisories@github.com
  - url: 'https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6j'
    label: security-advisories@github.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:6309'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6497'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6567'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6568'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6720'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6912'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-28498'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2448182'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28498.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-28498'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-28498'
tags:
  - nvd
  - cve.org
  - exploit-available
  - csaf
  - vex
  - red-hat
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-03-16T18:14:21.039703Z'
scores:
  nvd: 7.5
  cna: 8.2
  vendor: 9.1
epss: 0.00257
epssPercentile: 0.15532
ingestedAt: '2026-07-01T15:50:58.716Z'
---

## Overview

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.

## Affected

- `authlib < 1.6.9`

## Remediation

Upgrade past the affected range:

- `authlib 1.6.9`

## Vendor advisories

- **RHSA-2026:6309** · Red Hat · fixed in: Red Hat Ansible Automation Platform 2.6 · released 2026-03-31 · [advisory](https://access.redhat.com/errata/RHSA-2026:6309)
- **RHSA-2026:6912** · Red Hat · fixed in: Red Hat Quay 3.10 · released 2026-04-07 · [advisory](https://access.redhat.com/errata/RHSA-2026:6912)
- **RHSA-2026:6720** · Red Hat · fixed in: Red Hat Quay 3.12 · released 2026-04-06 · [advisory](https://access.redhat.com/errata/RHSA-2026:6720)
- **RHSA-2026:6568** · Red Hat · fixed in: Red Hat Quay 3.15 · released 2026-04-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:6568)
- **RHSA-2026:6497** · Red Hat · fixed in: Red Hat Quay 3.16 · released 2026-04-02 · [advisory](https://access.redhat.com/errata/RHSA-2026:6497)
- **RHSA-2026:6567** · Red Hat · fixed in: Red Hat Quay 3.16 · released 2026-04-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:6567)
- **Red Hat VEX** · Important · affected: Red Hat Ansible Automation Platform 2, Red Hat Satellite 6 · no fix planned: Red Hat Ansible Automation Platform 2, Red Hat Satellite 6 · updated 2026-09-09 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28498.json)