Directory traversal vulnerability in models/Cart66.php in the Cart66 Lite plugin before 1.5.4 for WordPress allows remote authenticated users to read arbitrary files via a .. (dot dot) in the member_download action to wp-admin/admin-ajax.php.
https://wordpress.org/plugins/cart66-lite/changelog/
https://plugins.trac.wordpress.org/changeset/1052064/cart66-lite