CVE-2026-27659: CSRF vulnerability in UpdateAccessControlPolicyActiveStatus endpoint
Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to properly validate CSRF tokens in the /api/v4/accesscontrolpolicies/{policyid}/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a crafted request.. Mattermost Advisory ID: MMSA-2026-00578
Affected Software
Remediation
Information
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27659?
CVE-2026-27659 is a medium severity Cross-Site Request Forgery (CSRF) vulnerability.
How do I fix CVE-2026-27659?
To fix CVE-2026-27659, upgrade Mattermost to versions 11.2.3, 10.11.11, 11.4.1, or 11.3.2 or later.
Which versions of Mattermost are affected by CVE-2026-27659?
Affected versions by CVE-2026-27659 include Mattermost 11.2.x up to 11.2.2, 10.11.x up to 10.11.10, 11.4.x up to 11.4.0, and 11.3.x up to 11.3.1.
What type of vulnerability is CVE-2026-27659?
CVE-2026-27659 is classified as a Cross-Site Request Forgery (CSRF) vulnerability.
What endpoint is impacted by CVE-2026-27659?
CVE-2026-27659 impacts the /api/v4/access_control_policies/{policy_id}/activate endpoint in Mattermost.