The WPFunnels WordPress plugin before 3.13.0 does not perform any authorisation or nonce check in one of its opt-in submission handlers, and takes the notification recipients and subject from the request, allowing unauthenticated users to make the site send emails to arbitrary recipients with an arbitrary subject.
https://wpscan.com/vulnerability/45abb077-c4ed-472e-8658-443506605235/