CVE-2018-21252: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.6% chance of exploitation in the next 30 days.

An issue was discovered in Mattermost Server before 5.2, 5.1.1, 5.0.3, and 4.10.3. Attackers could use multiple e-mail addresses to bypass a domain-based policy for signups.

Affected products

• Mattermost Mattermost Server: before 4.10.3 (fixed in 4.10.3); from 5.0.0, before 5.0.3 (fixed in 5.0.3); from 5.1.0, before 5.1.1 (fixed in 5.1.1); version 5.2.0 only

Published 2020-06-19. Last modified 2026-06-17.