CVE-2025-11777: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.2% chance of exploitation in the next 30 days.

Mattermost versions 10.11.x <= 10.11.3, 10.5.x <= 10.5.11 fail to properly validate team membership permissions in the Add Channel Member API which allows users from one team to access user metadata and channel membership information from other teams via the API endpoint

Affected products

• Mattermost Mattermost Server: from 10.5.0, before 10.5.12 (fixed in 10.5.12); from 10.11.0, before 10.11.4 (fixed in 10.11.4)

Published 2025-11-13. Last modified 2026-06-17.