[Sprakle]

It was my understanding that iOS devices have kernel or hardware checks prevent unsigned code from running. This is why JIT languages don't work there.

Is that true? If so, how to remote code execution exploits like this work?

[saagarjha]

Correct, most processes on iOS do not have the ability to JIT code. Usually exploits such as these rely on return oriented programming techniques (https://en.wikipedia.org/wiki/Return-oriented_programming) to bypass this, although Apple has added hardware mitigations for this in its newer chips.

[lawnchair_larry]

The point of pretty much all exploits is to find ways to bypass that very feature.