LaunchServices in Apple Mac OS X before 10.9 does not properly restrict Unicode characters in filenames, which allows context-dependent attackers to spoof file extensions via a crafted character sequence.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-5018
http://support.apple.com/kb/HT6150
http://lists.apple.com/archives/security-announce/2013/Oct/msg00004.html