The FPW Category Thumbnails plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'id' parameter of the 'fpw_fs_get_file' AJAX action in all versions up to, and including, 1.9.5. This is due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with Subscriber-level access and above, to inject arbitrary web scripts in pages that will execute whenever an administrator accesses the plugin's settings page.