Apple Mac OS X before 10.7.5 does not properly handle the bNbrPorts field of a USB hub descriptor, which allows physically proximate attackers to execute arbitrary code or cause a denial of service (memory corruption and system crash) by attaching a USB device.
https://exchange.xforce.ibmcloud.com/vulnerabilities/78750
http://support.apple.com/kb/HT5501
http://lists.apple.com/archives/security-announce/2012/Sep/msg00004.html