CVE-2026-3636: Mattermost Server

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

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to sanitize team member data when returned via API to users without elevated permissions which allows a user without permissions to get data about team members roles via invoking various team API endpoints.. Mattermost Advisory ID: MMSA-2026-00626

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.15 (fixed in 10.11.15); from 11.4.0, before 11.4.5 (fixed in 11.4.5); from 11.5.0, before 11.5.4 (fixed in 11.5.4); from 11.6.0, before 11.6.1 (fixed in 11.6.1)

Published 2026-05-22. Last modified 2026-07-23.