Checkm8: unpatchable iOS exploit could lead to permanent jailbreak for iOS devices running A5 to A11 chips

Pierluigi Paganini September 27, 2019

A security expert has released a new jailbreak, dubbed Checkm8, that impacts all iOS devices running on A5 to A11 chipsets, it works on iPhone models from 4S to 8 and X.

The security expert Axi0mX has released a new jailbreak, dubbed Checkm8, that works on all iOS devices running on A5 to A11 chipsets. The jailbreak works with all Apple products released between 2011 and 2017, including iPhone models from 4S to 8 and X.

Checkm8 leverages vulnerabilities in the Apple Bootrom (secure boot ROM) to achieve full control over their device.

“The bootrom (called “SecureROM” by Apple) is the first significant code that runs on an iDevice. The bootrom is read-only. Finding exploits in the bootrom level is a big achievement since Apple won’t be able to fix it without a hardware revision.” reads a description for the BootRom.

The expert who devised the Checkm8 jailbreak described it as “a permanent unpatchable bootrom exploit,” anyway it is essential to highlight that the exploit could lead to a jailbreak by chaining it with other flaws.

Bootrom jailbreaks are very dangerous because they are permanent and can’t be addressed via software, in order to patch a Bootrom flaw it is necessary to physical modify the chipsets.

Axi0mX’s jailbreak code is marked as a “beta” release, but there is the concrete possibility that experts coders or intelligence agencies will integrate it in hacking tools and malware.

“What I am releasing today is not a full jailbreak with Cydia, just an exploit. Researchers and developers can use it to dump SecureROM, decrypt keybags with AES engine, and demote the device to enable JTAG. You still need additional hardware and software to use JTAG.” wrote the expert.

“Features the exploit allow include:

  • Jailbreak and downgrade iPhone 3GS (new bootrom) with alloc8 untethered bootrom exploit. 🙂
  • Pwned DFU Mode with steaks4uce exploit for S5L8720 devices.
  • Pwned DFU Mode with limera1n exploit for S5L8920/S5L8922 devices.
  • Pwned DFU Mode with SHAtter exploit for S5L8930 devices.
  • Dump SecureROM on S5L8920/S5L8922/S5L8930 devices.
  • Dump NOR on S5L8920 devices.
  • Flash NOR on S5L8920 devices.
  • Encrypt or decrypt hex data on a connected device in pwned DFU Mode using its GID or UID key.

Currently, the jailbreak does not work on Apple’s latest two A12 and A13 chipsets.

Experts pointed out that the jailbreak needs physical access to the device, so and could not be used remotely.

“During iOS 12 betas in summer 2018, Apple patched a critical use-after-free vulnerability in iBoot USB code. This vulnerability can only be triggered over USB and requires physical access. It cannot be exploited remotely. I am sure many researchers have seen that patch.” concludes the expert.

“That’s how I discovered it. It is likely at least a couple other researchers were able to exploit this vulnerability after discovering the patch. The patch is easy to find, but the vulnerability is not trivial to exploit on most devices.”

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Pierluigi Paganini

(SecurityAffairs – Checkm8, hacking)

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