In a significant revelation, security experts from Paradigm Shift have identified a critical BootROM vulnerability affecting two of Apple's legacy A-series processors, the A12 Bionic and A13 Bionic. Devices powered by these chips, such as the iPhone XR, XS, XS Max, and the iPhone 11 lineup, may be at risk of exploitation due to this flaw which is embedded within the hardware itself.
Understanding the BootROM Vulnerability in Apple Devices
The BootROM, or SecureROM, is the initial code executed when an iPhone is powered on. Typically, Apple mitigates software vulnerabilities through updates; however, because BootROM flaws are hardcoded into the chip during manufacturing, there is no avenue for a software patch to resolve this issue.
This vulnerability is reminiscent of the "checkm8" exploit discovered in 2019, which targeted processors from the iPhone 4S through to the iPhone X. The current issue, dubbed "usbliter8," affects processors within the iPhone XS through iPhone 11 series models.
Nature of the BootROM Flaw: A USB Controller Issue
The discovered vulnerability stems from a bug in the USB controller hardware, not from Apple's software. When a susceptible iPhone boots, it receives USB data as small packets, which are usually directed to appropriate memory buffers by the USB controller. However, due to this flaw, certain maliciously crafted packet patterns can misdirect the memory pointer, allowing data to be written to unintended areas, potentially enabling the execution of unauthorized code.
Security Implications: User Data is Safe
Despite the potential for exploitation, researchers have assured that passcodes and encrypted user data remain protected, even if the vulnerability is taken advantage of. The usbliter8 flaw grants attackers the ability to load modified software on affected devices before the iOS system initializes.
Recommended Countermeasure: Upgrade Needed
Paradigm Shift recommends that the only effective countermeasure against this vulnerability is to upgrade to newer iPhone models. The A11 Bionic and later processors have a reset pointer feature after each packet, eliminating this vulnerability.
The following is a list of affected iPhone models that are susceptible to the "checkm8" and "usbliter8" BootROM variations:
- iPhone 4S (A5)
- iPhone 5 (A6)
- iPhone 5c (A6)
- iPhone 5s (A7)
- iPhone 6 & 6 Plus (A8)
- iPhone 6s & 6s Plus (A9)
- iPhone SE (1st Generation) (A9)
- iPhone 7 & 7 Plus (A10 Fusion)
- iPhone 8 & 8 Plus (A11 Bionic)
- iPhone X (A11 Bionic)
- iPhone XR (A12 Bionic)
- iPhone XS (A12 Bionic)
- iPhone XS Max (A12 Bionic)
- iPhone 11 (A13 Bionic)
- iPhone 11 Pro (A13 Bionic)
- iPhone 11 Pro Max (A13 Bionic)
- iPhone SE (2nd generation - A13 Bionic)
