CVE-2026-3115: Mattermost Server

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

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 apply view restrictions when retrieving group member IDs, which allows authenticated guest users to enumerate user IDs outside their allowed visibility scope via the group retrieval endpoint.. Mattermost Advisory ID: MMSA-2026-00594

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.11 (fixed in 10.11.11); from 11.2.0, before 11.2.3 (fixed in 11.2.3); from 11.3.0, before 11.3.2 (fixed in 11.3.2); version 11.4.0 only

Published 2026-03-26. Last modified 2026-06-17.