CVE-2025-6465: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.8% chance of exploitation in the next 30 days.

Mattermost versions 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 10.10.x <= 10.10.0, 10.9.x <= 10.9.3 fail to sanitize file names which allows users with file upload permission to overwrite file attachment thumbnails via path traversal in file streaming APIs.

Affected products

• Mattermost Mattermost Server: from 10.5.0, before 10.5.9 (fixed in 10.5.9); from 10.8.0, before 10.8.4 (fixed in 10.8.4); from 10.9.0, before 10.9.4 (fixed in 10.9.4); version 10.10.0 only

Published 2025-08-21. Last modified 2026-06-17.