GHSA-5FWX-P6XH-VJRH Mattermost allows reading arbitrary files related to importing boards

Mattermost versions 10.4.x = 10.4.1, 9.11.x = 9.11.7, 10.3.x = 10.3.2, 10.2.x = 10.2.2 fail to properly validate board blocks when importing boards which allows an attacker could read any arbitrary file on the system via importing and exporting a specially crafted import archive in Boards...