Summary
The target is running at least one instance of Simple Form which fails to validate the parameters 'admin_email_to' and 'admin_email_from'.
An attacker, exploiting this flaw, would be able to send email through the server (utilizing the form) to any arbitrary recipient with any arbitrary message content. In other words, the remote host can be used as a mail relay for things like SPAM.
Solution
Upgrade to Simple Form 2.2 or later.
References
Updated on 2015-03-25