From: Apple Product Security
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APPLE-SA-2015-06-30-3 Mac EFI Security Update 2015-001

Mac EFI Security Update 2015-001 is now available and addresses the
following:

EFI
Available for:  OS X Mountain Lion v10.8.5, OS X Mavericks v10.9.5
Impact:  A malicious application with root privileges may be able to
modify EFI flash memory [...]