CVE-2026-6739: Mattermost Server

High severity, CVSS 7.2. EPSS: 0.5% chance of exploitation in the next 30 days.

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to require system-level permission when patching protected default system roles, which allows authenticated users with delegated user-management permissions to escalate privileges by altering built-in role permissions via the role patch API.. Mattermost Advisory ID: MMSA-2026-00656

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.17 (fixed in 10.11.17); from 11.5.0, before 11.5.5 (fixed in 11.5.5); from 11.6.0, before 11.6.2 (fixed in 11.6.2)

Published 2026-06-12. Last modified 2026-06-18.