Mattermost Fails to Validate File Paths

Mattermost versions 10.9.x = 10.9.1, 10.8.x = 10.8.3, 10.5.x = 10.5.8, 9.11.x = 9.11.17 fail to properly validate file paths during plugin import operations which allows restricted admin users to install unauthorized custom plugins via path traversal in the import functionality, bypassing plugin...