YesWiki before 4.6.7 Unauthenticated Open Mail Relay via Contact Mail Handler

YesWiki before 4.6.7 contains an authentication bypass in the contact mail AJAX handler that allows unauthenticated attackers to send email through the wiki's SMTP server. Attackers can POST an XMLHttpRequest to the mail handler without field or type parameters, supplying arbitrary recipient, sender, subject and body for spam and phishing.