CVE-2025-9078: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.2% chance of exploitation in the next 30 days.

Mattermost versions 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 9.11.x <= 9.11.17, 10.10.x <= 10.10.1, 10.9.x <= 10.9.3 fail to properly validate cache keys for link metadata which allows authenticated users to access unauthorized posts and poison link previews via hash collision attacks on FNV-1 hashing

Affected products

• Mattermost Mattermost Server: from 9.11.0, before 9.11.18 (fixed in 9.11.18); 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); from 10.10.0, before 10.10.2 (fixed in 10.10.2)

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