BackWPup < 5.5.1 - Missing Authorization to Sensitive Information Exposure

Description

The plugin is vulnerable to unauthorized access of data due to a missing capability check on the 'backwpup_working' AJAX action. This makes it possible for authenticated attackers, with Subscriber-level access and above, to retrieve access to a back-up's filename while a backup is running. This information has little value on it's own, but could be used to aid in a brute force attack to retrieve back-up contents in limited environments (i.e. NGINX).