CVE-2018-21256: 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 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.

Affected products

• Mattermost Mattermost Server: before 5.1.0 (fixed in 5.1.0)

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