CVE-2019-20855: Mattermost Server

High severity, CVSS 7.5. EPSS: 1.2% chance of exploitation in the next 30 days.

An issue was discovered in Mattermost Server before 5.16.1, 5.15.2, 5.14.5, and 5.9.6. It allows attackers to obtain sensitive information (local files) during legacy attachment migration.

Affected products

• Mattermost Mattermost Server: before 5.9.6 (fixed in 5.9.6); from 5.14.0, before 5.14.5 (fixed in 5.14.5); from 5.15.0, before 5.15.2 (fixed in 5.15.2); from 5.16.0, before 5.16.1 (fixed in 5.16.1)

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