CVE-2019-20866: Mattermost Server

Medium severity, CVSS 5.3. EPSS: 0.9% chance of exploitation in the next 30 days.

An issue was discovered in Mattermost Server before 5.12.0. Use of a Proxy HTTP header, rather than the source address in an IP packet header, for obtaining IP address information was mishandled.

Affected products

• Mattermost Mattermost Server: before 5.12.0 (fixed in 5.12.0)

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