CVE-2025-10545: Mattermost Server

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

Mattermost versions 10.5.x <= 10.5.10, 10.11.x <= 10.11.2 fail to properly validate guest user permissions when adding channel members which allows guest users to add any team members to their private channels via the `/api/v4/channels/{channel_id}/members` endpoint

Affected products

• Mattermost Mattermost Server: from 10.5.0, before 10.5.11 (fixed in 10.5.11); from 10.11.0, before 10.11.3 (fixed in 10.11.3)

Published 2025-10-16. Last modified 2026-06-17.