Keep Backup Daily <= 2.1.1 - Authenticated (Admin+) Limited Path Traversal via 'kbd_path' Parameter

The Keep Backup Daily plugin for WordPress is vulnerable to Limited Path Traversal in all versions up to, and including, 2.1.1 via the `kbd_open_upload_dir` AJAX action. This is due to insufficient validation of the `kbd_path` parameter, which is only sanitized with `sanitize_text_field()` - a function that does not strip path traversal sequences. This makes it possible for authenticated attackers, with Administrator-level access and above, to list the contents of arbitrary directories on the server outside of the intended uploads directory.