The The WP Popup Builder – Popup Forms and Marketing Lead Generation plugin for WordPress is vulnerable to arbitrary shortcode execution via the wp_ajax_nopriv_shortcode_Api_Add AJAX action in all versions up to, and including, 1.3.5. This is due to the software allowing users to execute an action that does not properly validate a value before running do_shortcode. This makes it possible for unauthenticated attackers to execute arbitrary shortcodes. NOTE: This vulnerability was partially fixed in version 1.3.5 with a nonce check, which effectively prevented access to the affected function. However, version 1.3.6 incorporates the correct authorization check to prevent unauthorized access.