Apple Mac EFI before 2015-001, as used in OS X before 10.10.4 and other products, does not enforce a locking protection mechanism upon being woken from sleep, which allows local users to conduct EFI flash attacks by leveraging root privileges.
Apple Security Advisory 2015-06-30-3 - Mac EFI Security Update 2015-001 is now available and addresses EFI flash memory modification and memory corruption issues.