Checkm8 Exploit Opens Door to Unpatchable Jailbreak on iPhone 4S Through iPhone X

A security researcher who goes by "axi0mX" on Twitter today released "checkm8," which he claims is a bootrom exploit for iOS devices equipped with A5 through A11 chips, including the iPhone 4S through iPhone X, several iPad models dating back to the iPad 2, and the fifth-generation iPod touch and later.

trio iphones ios
This would be the first publicly released bootrom exploit since the iPhone 4 in 2010 and pave the way for a permanent, non-patchable jailbreak on hundreds of millions of affected iOS devices. Since the bootrom is read-only, Apple cannot patch this type of exploit with a software update.


The bootrom exploit has many other possibilities on affected devices, including downgrading iOS versions without SHSH blobs or APTickets, dual booting iOS, and running custom firmwares, according to jailbreak enthusiasts.

This is significant news in the jailbreaking community, as the last bootrom exploit known as "limera1n" was released by George "geohot" Hotz nearly a decade ago for devices with A4 chips and earlier, including the iPhone 4, iPhone 3GS, the third- and fourth-generation iPod touch, and the original iPad.

Top Rated Comments

zorinlynx Avatar
15 months ago


This can't be good for the security of these devices...


And have malware installed or spying on you. No thanks. Apple should have gotten their sh** together and not have had the exploit open for nearly a week.

This is a bootrom exploit. It can only be exploited when the device is in DFU recovery mode and will not affect the security of devices being used normally.

This is really the best kind of jailbreak exploit because only the people who really want to go out of their way to jailbreak can use it. Regular users are safe; all it means is that people can do whatever they like with these devices they own now.
Score: 35 Votes (Like | Disagree)
itsmilo Avatar
15 months ago


All the cool kids violate their warranty. Didn't you know?

one restore on iTunes and your warranty is „restored“ so to speak
Score: 28 Votes (Like | Disagree)
tobefirst Avatar
15 months ago
I haaaaaaate the new force press/haptic touch menu on iOS 13. I would consider jail breaking just to go back to how that worked on my X on iOS 12.
Score: 16 Votes (Like | Disagree)
Jeremy1026 Avatar
15 months ago
I haven't been jailbroken since the 3G, what's the big draw of a jailbreak now a days?
Score: 15 Votes (Like | Disagree)
redheeler Avatar
15 months ago
Good, now we can have proper downgrade rights on these devices. It's sad that something like this is needed to, for example, downgrade to iOS 10 on an iPad Air 2 for the simple purpose of running 32-bit apps.
Score: 14 Votes (Like | Disagree)
Krevnik Avatar
15 months ago


Once the data is copied off the phone can't you brute force it without fear of being locked out? What's the encryption like?

You can read through the details yourself if you want: https://www.apple.com/business/docs/site/iOS_Security_Guide.pdf

The NAND itself is encrypted with AES 256. The passcode is the weak point, but to generate the AES 256 key from the passcode, you need the passcode and the unique AES 256 key burned into the Secure Enclave on the SOC. The passcode is run through PBKDF2 and then tangled with the AES 256 key in a one-way operation.

So dumping the flash raw means you face AES 256 at full strength, even if you know the passcode, because you also need the AES 256 key from the SOC to be able to recreate the key yourself if you aren't just brute forcing AES.

The fastest way to crack an iPhone is to brute force the passcode and bypass the lockout on attempts if you can. It also gives you the most access to the content.

Individual containers/files can be encrypted with separate keys based on the level of access the OS should have in different states of lock/unlock, on top of the NAND encryption. So if you dump the flash unencrypted, you then also need to crack the containers for things like email and messages which are also AES 256 encryption. All the more reason to focus even more on the passcode and attempt lockout mechanisms.


This is a bootROM exploit. Every iPhone ever manufactured excluding the iPhone XS and 11 series will always be vulnerable to this exploit regardless of any iOS updates. There is no patch.

Apple still manufactures the iPhone 8 and 3rd Gen Air. I wouldn't be surprised if we see manufacturing runs of those that include the patched boot ROM.
Score: 14 Votes (Like | Disagree)

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