Macs older than a year are vulnerable to exploits that remotely overwrite the firmware that boots up the machine, a feat that allows attackers to control vulnerable devices from the very first instruction.
The attack, according to a blog post published Friday by well-known OS X security researcher Pedro Vilaca, affects Macs shipped prior to the middle of 2014 that are allowed to go into sleep mode. He found a way to reflash a Mac's BIOS using functionality contained in userland, which is the part of an operating system where installed applications and drivers are executed. By exploiting vulnerabilities such as those regularly found in Safari and other Web browsers, attackers can install malicious firmware that survives hard drive reformatting and reinstallation of the operating system.
The attack is more serious than the Thunderstrike proof-of-concept exploit that came to light late last year. While both exploits give attackers the same persistent and low-level control of a Mac, the new attack doesn't require even brief physical access as Thunderstrike did. That means attackers half-way around the world may remotely exploit it.