The Contact Form by Bit Form: Multi Step Form, Calculation Contact Form, Payment Contact Form & Custom Contact Form builder plugin for WordPress is vulnerable to arbitrary JavaScript file uploads due to missing input validation in the addCustomCode function in versions 2.0 to 2.13.9. This makes it possible for authenticated attackers, with Administrator-level access and above, to upload arbitrary JavaScript files to the affected site's server.
https://plugins.trac.wordpress.org/browser/bit-form/tags/2.13.6/includes/Admin/AdminAjax.php#L1314