security

Owners of affected iPhones can stop checking for patches now: the fix for this SecureROM bug comes in a new handset

A newly disclosed BootROM exploit affecting Apple's A12 and A13 chips gives researchers a way to break the secure boot chain on millions of iPhones and other Apple devices.

The exploit, dubbed “usbliter8” by security researchers at Paradigm Shift, targets a flaw in the SecureROM code found on the iPhone XS, XR, 11, and 11 Pro models, plus other devices powered by Apple's A12 and A13 processors. Because the vulnerability resides in immutable BootROM code burned into silicon during manufacturing, it cannot be patched. 

The researchers traced the issue to the Synopsys DesignWare USB controller used by Apple. A flaw in how the hardware handles certain USB setup packets allows attackers to corrupt memory during Device Firmware Update (DFU) mode, and ultimately gain control of SecureROM itself.

That might sound like an unremarkable minor moment in boot process, but SecureROM sits at the very bottom of Apple's chain of trust. If an attacker can compromise it, they can interfere with everything that comes afterward.

For ordinary iPhone owners, there is little reason to panic. Exploitation requires physical access to a device and the ability to place it into DFU mode, which means this isn’t the sort of bug criminals are likely to weaponize in phishing campaigns or drive-by attacks.

For security researchers, however, BootROM vulnerabilities are the gift that keeps on giving. Unlike software flaws that disappear after the next patch Tuesday, these bugs remain exploitable for the lifetime of the hardware.

Paradigm’s proof-of-concept demonstrates the ability to run unsigned code during the boot process, load custom iBoot images without signature checks, and modify DFU behavior. The exploit also marks compromised devices with the traditional "PWND" - a string familiar to anyone who spent time around the jailbreaking community over the last decade.

Not every generation of iPhone has the flaw. According to the researchers, Apple's A11 chips dodge the issue thanks to a different USB implementation, while A14 and later hardware appears to have fixed the conditions that make the exploit possible in the first place.

“While newer generations have addressed the underlying issue, affected A12 and A13 devices will carry it for the remainder of their lifetime,” said Paradigm researchers. “For those who have followed the history of iPhone exploitation and jailbreaking, this research is a reminder that the BootROM still occasionally has a surprise left to give.

The team said it disclosed the findings to Apple before publication and coordinated the release of the research with the company. Apple did not respond to The Register’s request for comment. 

The exploit doesn’t directly compromise Apple's Secure Enclave Processor, which remains responsible for protecting passcodes, encryption keys, and other sensitive data. Still, gaining control of SecureROM is about as close as researchers can get to the keys to the kingdom without crossing that final boundary.

There's no fix, but a remedy is simple, if somewhat expensive: buy a new iPhone.  ®