Apple's T2 safety chip has an unrecoverable bug


Enlarge /. The 2014 Mac mini is pictured here alongside the 2012 Mac mini. They looked the same, but the insides were different in a few important – and disappointing – ways.

A recently released With this tool, anyone can take advantage of an uncommon Mac vulnerability to bypass Apple's trusted T2 security chip and gain full system access. The bug is one that researchers have been using to jailbreak older models of iPhones for more than a year. The fact that the T2 chip is vulnerable in the same way creates a new host of potential threats. Worst of all, Apple can potentially slow down potential hackers. Ultimately, however, the error cannot be fixed on every Mac that has a T2 on it.

In general, the jailbreak community hasn't paid as much attention to macOS and OS X as iOS because they don't have the same restrictions and walled gardens built into Apple's mobile ecosystem. However, the T2 chip introduced in 2017 brought with it some limitations and puzzles. Apple added the chip as a trusted mechanism for securing high value features like encrypted data storage, Touch ID and Activation Lock that work with Apple's "Find My" services. However, the T2 also contains a security flaw called Checkm8, which jailbreakers are already exploiting in Apple's mobile chipsets A5 to A11 (2011 to 2017). Now Checkra1n, the same group that developed the tool for iOS, has released support for T2 bypass.

On Macs, researchers can use the jailbreak to examine the T2 chip and examine its security features. It can even be used to run Linux on the T2 or play Doom on the Touch Bar on a MacBook Pro. However, the jailbreak could also be armed by malicious hackers to disable macOS security features like System Integrity Protection and Secure Boot and install malware. Combined with another T2 vulnerability publicly announced in July by the Chinese security research and jailbreaking group Pangu Team, the jailbreak could potentially also be used to obtain FileVault encryption keys and decrypt user data. The vulnerability cannot be resolved because the flaw resides in immutable code for low-level hardware.

"The T2 is meant to be that little secure black box on Macs – a computer inside your computer that does things like lost mode enforcement, integrity checks, and other privileged tasks," said Will Strafach, longtime iOS researcher and inventor of the Guardian Firewall -App for iOS. "So the meaning is that this chip should be harder to compromise – but now it's done."

Apple did not respond to WIRED's request for comment.

Some restrictions

However, there are a few key limitations to jailbreaking that keep it from being a full-blown security crisis. The first is that an attacker would need physical access to target devices in order to exploit them. The tool can only be run from another device via USB. This means that hackers cannot remotely infect any Mac with a T2 chip. An attacker could jailbreak a target device and then disappear, but the compromise is not "persistent". It ends when the T2 chip is restarted. However, the Checkra1n researchers warn that the T2 chip itself does not restart every time the device does this. To ensure that a Mac was not jailbroken, the T2 chip must be completely reset to Apple's default settings. After all, jailbreaking does not give an attacker instant access to a target's encrypted data. It could allow hackers to install keyloggers or other malware that could later retrieve the decryption keys, or it could be easier to brutally enforce, but Checkra1n is not a silver bullet.

"There are many other vulnerabilities, including remote vulnerabilities that undoubtedly have more security implications," a Checkra1n team member tweeted Tuesday.

In a discussion with WIRED, the Checkra1n researchers added that they consider jailbreaking a necessary tool for the transparency of T2. "It's a unique chip that is different from iPhones. So Open Access is helpful in understanding it on a deeper level," said one group member. "It used to be a complete black box and now we can examine it and find out how it works for security research."

No surprise

The exploit isn't a surprise either; Since the original Checkm8 discovery last year, the T2 chip has been shown to be vulnerable in the same way. And researchers point out that while the T2 chip debuted in top-tier iMacs in 2017, it was only recently introduced across the Mac line. Older Macs with a T1 chip are not affected. The result matters, however, as it undermines a crucial security feature found in newer Macs.

Jailbreaking has long been a gray area because of this tension. It gives users the freedom to install and change anything they want on their devices. However, this is achieved by exploiting vulnerabilities in the Apple code. Hobbyists and researchers use jailbreaks in a constructive way, including to conduct more security tests and potentially help Apple fix more bugs. However, there is always the possibility that attackers could use jailbreaks for damage.

"I had already assumed that T2 was toast because it was prone to Checkm8," said Patrick Wardle, Apple security researcher at the enterprise management firm Jamf and a former NSA researcher. "There's really not much Apple can do to fix this. It's not the end of the world, but this chip that was supposed to provide all that extra security is now pretty controversial."

Wardle points out that for companies that use Apple's Activation Lock and Find My features to manage their devices, jailbreaking can be particularly problematic in terms of both potential device theft and other insider threats. And he notes that the jailbreak tool could be a valuable starting point for attackers looking for a shortcut to developing potentially powerful attacks. "You could probably use this as a weapon and create a neat in-memory implant that naturally disappears when you restart," he says. This means that the malware runs without a trace and is difficult for victims to find.

However, the situation poses much deeper problems as the basic approach is to use a special, trusted chip to secure other processes. In addition to Apple's T2, numerous other technology providers have tried this approach and defeated their secure enclaves, including Intel, Cisco, and Samsung.

"Always a double-edged sword"

"The implementation of hardware security mechanisms is always a double-edged sword," says Ang Cui, founder of the embedded device security company Red Balloon. "If an attacker is able to have the secure hardware mechanism, the defender usually loses more than if he hadn't built any hardware. In theory, it's a smart design, but in the real world it usually fails."

In that case you would probably have to be a very high quality target to register a real alarm. However, hardware-based security measures cause a single point of failure on which the most important data and systems rely. Even if the Checkra1n jailbreak does not give attackers unrestricted access, it offers them more than anyone would like.

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Steven Gregory