The CPU Software in Apple OS X before 10.10.2 allows physically proximate attackers to modify firmware during the EFI update process by inserting a Thunderbolt device with crafted code in an Option ROM, aka the "Thunderstrike" issue.
https://trmm.net/Thunderstrike
http://www.securitytracker.com/id/1031650
http://support.apple.com/HT204244
http://lists.apple.com/archives/security-announce/2015/Jan/msg00003.html