Apple Remote Desktop before 3.7 does not properly use server authentication-type information during decisions about whether to present an unencrypted-connection warning message, which allows remote attackers to obtain sensitive information in opportunistic circumstances by sniffing the network during an unintended cleartext VNC session.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-4976
http://lists.apple.com/archives/security-announce/2013/Oct/msg00008.html