The Motors – Car Dealership & Classified Listings Plugin plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'stm_f_s' parameter in all versions up to, and including, 1.4.123 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 a user accesses an injected page. The nonce required by the stm_ajax_add_a_car AJAX handler is emitted in wp_footer on every page, making it accessible to any authenticated user and removing any practical barrier to exploitation at the Subscriber level.