The The WPB Popup for Contact Form 7 – Showing The Contact Form 7 Popup on Button Click – CF7 Popup plugin for WordPress is vulnerable to arbitrary shortcode execution via wpb_pcf_fire_contact_form AJAX action in all versions up to, and including, 1.7.5. 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.
https://wordpress.org/plugins/wpb-popup-for-contact-form-7/#developers
https://plugins.trac.wordpress.org/changeset/3188864/
https://gist.github.com/wpbean/1a5abfea883621b4e150eab1362a420f