CVE-2026-6341: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to have API-level checks on which groups the user can create issues or attach comments to which allows a user that is member of multiple groups to create issues to a locked group via direct API requests. Mattermost Advisory ID: MMSA-2026-00602

Affected products

• Mattermost Mattermost Server: from 10.13.0, up to and including 10.13.11; from 11.1.0, up to and including 11.1.5; from 11.3.0, up to and including 11.3.4

Published 2026-05-18. Last modified 2026-06-17.