CVE-2025-6227: Mattermost Server

Low severity, CVSS 3.1. EPSS: 0.2% chance of exploitation in the next 30 days.

Mattermost versions 10.5.x <= 10.5.7, 9.11.x <= 9.11.16 fail to negotiate a new token when accepting the invite which allows a user that intercepts both invite and password to send synchronization payloads to the server that originally created the invite via the REST API.

Affected products

• Mattermost Mattermost Server: from 9.11.0, before 9.11.17 (fixed in 9.11.17); from 10.5.0, before 10.5.8 (fixed in 10.5.8)

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