Jailbreaks was a thing of the past, but the first free, public iPhone jailbreak in years was released last month by a security research.

Now, another security researcher has found a feat that could allow any iPhone from the 2011 4S to the 2017 iPhone X and 8/Plus to be permanently jailed.

The bootrom exploit, dubbed checkm8, was revealed by the Twitter user axi0mX, which makes it possible to jail the devices. As explained by The Verge, bootrom exploits take advantage of an initial code vulnerability that iOS devices load when booting up. Because it's read-only memory (ROM), through a software update, Apple can not overwrite or patch it. It's permanent, in other words.

Luckily, the exploit requires physical access to a phone and needs to be done via USB, so while hundreds of millions of iPhones are at risk, many of them are unlikely to be affected.

As far as we know, the checkm8 exploit still has no jailbreak. But there is a risk of developing the exploit and not requiring physical access in the future, which could leave millions of devices vulnerable. We have contacted Apple for comments and if we hear anything, we will update the story