Apple iPhone is considered to be one of the most secure smartphones on the planet. However, it is not immune from threat vectors that could jailbreak the device. 

A newly discovered iOS exploit is so severe that it could lead to permanent jailbreak on hundreds of millions of iPhones. 

The exploit was discovered by researcher axi0mX and is being dubbed as “checkm8” (read checkmate). The bootrom vulnerability introduces permanent unpatchable exploit for hundreds of millions of active iOS devices.

The exploit affects iPhones powered by older Apple A5 chip to newer Apple A11 chipset. In other words, it affects devices ranging from iPhone 4S to iPhone 8 and iPhone X. 

The researcher explains that the exploit gives hackers deep access to iOS that Apple would be unable to block or patch with a future update. 

While jailbreaking has lost its sheen, this new exploit will make it the biggest success for the hacking community. As a bootrom exploit, it takes advantage of a security vulnerability in the initial code that iOS devices loaded when they boot up.

The researcher notes that since it is ROM (read-only memory), it cannot be overwritten or patched by Apple. This leaves millions of devices exposed to hack and permanent jailbreak. The last iOS device with a public bootrom exploit was the iPhone 4, which was released in 2010.