CVE-2023-4478: Mattermost Server

High severity, CVSS 8.2. EPSS: 0.5% chance of exploitation in the next 30 days.

Mattermost fails to restrict which parameters' values it takes from the request during signup allowing an attacker to register users as inactive, thus blocking them from later accessing Mattermost without the system admin activating their accounts.

Affected products

• Mattermost Mattermost Server: before 7.8.9 (fixed in 7.8.9); from 7.9.0, before 7.10.5 (fixed in 7.10.5); version 8.0.0 only

Published 2023-08-25. Last modified 2026-06-17.