CVE-2025-6226: Mattermost Server

Medium severity, CVSS 6.5. EPSS: 0.3% chance of exploitation in the next 30 days.

Mattermost versions 10.5.x <= 10.5.6, 10.8.x <= 10.8.1, 10.7.x <= 10.7.3, 9.11.x <= 9.11.16 fail to verify authorization when retrieving cached posts by PendingPostID which allows an authenticated user to read posts in private channels they don't have access to via guessing the PendingPostID of recently created posts.

Affected products

• Mattermost Mattermost Server: from 9.11.0, before 9.11.17 (fixed in 9.11.17); from 10.5.0, before 10.5.7 (fixed in 10.5.7); from 10.7.0, before 10.7.4 (fixed in 10.7.4); from 10.8.0, before 10.8.2 (fixed in 10.8.2)

Published 2025-07-18. Last modified 2026-06-17.