PixMagix <= 1.7.2 - Authenticated (Author+) Path Traversal in 'layers[].id' Parameter

The PixMagix – WordPress Image Editor plugin for WordPress is vulnerable to Directory Traversal in all versions up to, and including, 1.7.2 via the move_image_on_server function. This makes it possible for authenticated attackers, with author-level access and above, to write files with attacker-controlled content to arbitrary locations on the server. The unsanitized 'layers[].id' parameter is concatenated into a filesystem path and passed to PHP's copy() function, allowing traversal sequences (e.g. '../../') to escape the intended upload directory and write attacker-supplied file contents to arbitrary paths accessible by the web server process. The save_template REST endpoint is gated by the create_projects permission (edit_pixmagix + upload_files), which Author-level users hold by default after plugin activation, making this exploitable by any Author on sites running PixMagix.