CVE-2019-20888: Mattermost Server

High severity, CVSS 7.5. EPSS: 1.1% chance of exploitation in the next 30 days.

An issue was discovered in Mattermost Server before 5.7, 5.6.3, 5.5.2, and 4.10.5. It allows attackers to cause a denial of service (memory consumption) via an outgoing webhook or a slash command integration.

Affected products

• Mattermost Mattermost Server: before 4.10.5 (fixed in 4.10.5); from 5.5.0, before 5.5.2 (fixed in 5.5.2); from 5.6.0, before 5.6.3 (fixed in 5.6.3); version 5.7.0 only

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