The developer "Mattermost Inc." released updates on Oct 2nd & 3rd that fix several security-critical vulnerabilities in the products mobile & desktop app for "Mattermost".
The combination of closed vulnerabilities was given a CVSS-Basse score of 8.8 by the vendor.
Perform the latest update
Regularly check for available updates (possibly activate the automatic update)
Subscribing to the security newsletter of the manufacturer