CVE-2017-18889: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.7% chance of exploitation in the next 30 days.

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. An attacker could create fictive system-message posts via webhooks and slash commands, in the v3 or v4 REST API.

Affected products

• Mattermost Mattermost Server: before 4.1.2 (fixed in 4.1.2); from 4.2.0, before 4.2.1 (fixed in 4.2.1); version 4.3.0 only

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