From: Apple Product Security
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APPLE-SA-2015-10-21-6 Mac EFI Security Update 2015-002

Mac EFI Security Update 2015-002 is now available and addresses the
following:

EFI
Available for:  OS X Mavericks v10.9.5
Impact:  An attacker can exercise unused EFI functions
Description:  An issue existed with EFI argument handling. [...]