JetFormBuilder < 3.6.5.2 - Unauthenticated Email Header Injection via Send Email Action

The JetFormBuilder WordPress plugin before 3.6.5.2 does not validate or strip line breaks from address values it sources from submitted form fields before adding them to the headers of the e-mails it sends, allowing unauthenticated users to inject arbitrary e-mail headers, add hidden recipients and spoof the sender. Exploitation requires the site to be configured to take one of the message's addresses from a form field.