CVE-2025-9076: Mattermost Server

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

Mattermost versions 10.10.x <= 10.10.1 fail to properly sanitize user data during shared channel membership synchronization, which allows malicious or compromised remote clusters to access sensitive user information via unsanitized user objects. This vulnerability affects Mattermost Server instances with shared channels enabled.

Affected products

• Mattermost Mattermost Server: from 10.10.0, before 10.10.2 (fixed in 10.10.2)

Published 2025-09-15. Last modified 2026-06-17.