Apple firmware is now bundled with automatic updates to limit the chance of Thunderstrike-type breaches and improve overall security. However, researchers from Duo Security discovered that not all Macs contain the expected extensible firmware interface (EFI) version, putting them at risk of crippling, sub-OS attacks. What’s the root of this piecemeal protection, and how can users stay safe?
A Not-So-Firm Foundation?
Firmware exists below the MacOS and hypervisors but on top of hardware. Changes to firmware endure even after reboots, reimaging and complete OS removal, providing a consistent experience for users but also opening a significant attack avenue for malicious actors.
As noted by Fortune, EFI is the first component to boot after the device is turned on, giving fraudsters virtually unlimited access and making compromised devices effectively unsalvageable. Since attackers control the firmware, they can prevent any new versions from being installed.
In 2015, the Thunderstrike bootkit began specifically targeting Mac EFIs, prompting Apple to bundle firmware with automatic security updates. The intention was to improve overall safety by reducing the risk of failure-prone firmware.
However, according to Duo Security’s research, 4.2 percent of all Macs in production environments aren’t running the right EFI version. Specific cases are even worse, with 43 percent of 21.5-inch iMacs from late 2015 showing an Apple firmware mismatch.
Duo Security discovered that some EFI versions were incorrect and that the automatic update process didn’t provide any notification of the update failure. In other words, systems were unknowingly left exposed.
The researchers first contacted Apple, which immediately started working on a fix. Apple engineer Xeno Kovah noted in a since-deleted tweet that “we’ve got things we can do better,” according to the Fortune article.
Duo released the details of the vulnerability at the Ekoparty conference in Argentina last week. Expect designers of advanced persistent threats (APTs) to take notice and push new versions into the wild as soon as possible.
Fixing Apple Firmware Failures
While Apple hasn’t gone public with the reason for its firmware failures, 9to5Mac noted that the technology giant released a new OS version: MacOS 10.13, also called High Sierra. It comes with a tool that automatically validates Mac firmware every week.
This won’t check whether the EFI version is up to date, but it will discover if the firmware has been compromised. Duo released a set of tools on Github to compare current and expected versions of EFI.
According to Time, High Sierra comes with its own potential problems. Patrick Wardle of security firm Synack recently demonstrated that it’s possible for attackers to compromise Keychain passwords if users download a compromised app and give it permission to operate. While this requires “explicit approval” from users, third-party, unsigned apps are becoming more common as Mac device owners prioritize functionality over security.
Apple firmware on any Mac laptop could be out of date, putting devices at risk of total compromise. High Sierra should help detect potential problems, but until Apple confirms a complete fix, users should regularly check to make sure their Apple devices have more than just piecemeal protection.