CVE-2018-21257: Mattermost Server

Medium severity, CVSS 5.3. EPSS: 0.8% 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 setting a channel header) via the Channel header slash command API.

Affected products

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

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