Apple has announced an EFI securtity update for Mac OS X 10.9.5, apparently due to LegbaCore/MITRE research.
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. This was addressed by removing the affected functions.
CVE-ID: CVE-2015-7035 : Corey Kallenberg, Xeno Kovah, John Butterworth, and Sam Cornwell of The MITRE Corporation, coordinated via CERT
Installation note: Mac EFI Security Update 2015-002 may be obtained from the Mac App Store.
In addition to this EFI update, Apple has released Multiple Security Updates: