QuickTime in Apple Mac OS X before 10.7.3 does not prevent access to uninitialized memory locations, which allows remote attackers to execute arbitrary code or cause a denial of service (application crash) via a crafted MP4 file.
http://support.apple.com/kb/HT5261
http://support.apple.com/kb/HT5130
http://lists.apple.com/archives/security-announce/2012/May/msg00005.html
http://lists.apple.com/archives/security-announce/2012/Feb/msg00000.html