Photo Gallery, Sliders, Proofing and Themes <= 4.5.5 - Authenticated (Custom+) Arbitrary File Deletion via 'task_list' and 'app_config' Parameters

The Photo Gallery, Sliders, Proofing and Themes – NextGEN Gallery plugin for WordPress is vulnerable to arbitrary file deletion due to insufficient file path validation in the handle_job function in all versions up to, and including, 4.5.5 This makes it possible for authenticated attackers, with custom-level access and above, to delete arbitrary files on the server, which can easily lead to remote code execution when the right file is deleted (such as wp-config.php). The 'NextGEN Manage gallery' capability required to reach the vulnerable endpoint is granted to Administrators by default but can be delegated to lower-privileged roles via the plugin's Roles screen.