The GiveWP WordPress plugin before 2.17.3 does not sanitise and escape the form_id parameter before outputting it back in the response of an unauthenticated request via the give_checkout_login AJAX action, leading to a Reflected Cross-Site Scripting
https://wpscan.com/vulnerability/87a64b27-23a3-40f5-a3d8-0650975fee6f