Format string vulnerability in Screen Sharing Server in Apple Mac OS X before 10.9 and Apple Remote Desktop before 3.5.4 allows remote attackers to execute arbitrary code via format string specifiers in a VNC username.
http://lists.apple.com/archives/security-announce/2013/Oct/msg00008.html
http://lists.apple.com/archives/security-announce/2013/Oct/msg00007.html
http://lists.apple.com/archives/security-announce/2013/Oct/msg00004.html