Mac EFI Update 2015-001: malicious root app may be able to modify EFI flash

Related CVE:

http://www.kb.cert.org/vuls/id/577140

Applies to (at least) some DELL computers as well.

TLDR: There's a bug in some UEFI BIOSes that don't set the read-only flag when a computer comes back from sleep, thus allowing a malicious program to silently reflash the BIOS

More detailed analysis: https://reverse.put.as/2015/05/29/the-empire-strikes-back-ap...