I remember back in the day when people would “Jailbreak” iPhones, but never really picked up on what they were doing other than that it let them do stuff that those of us with “non-jailbroken” iPhones couldn’t do.
Are they just booting another OS, e.g. android? Also: why haven’t I heard of it in a while? Is it not possible on newer iPhones?
Some of the jailbreaks could be performed simply by visiting a specific website. Bugs in the web browser in earlier versions of iOS would trigger something known as a buffer overflow. A very specially crafted web request could target a buffer overflow bug that could cause arbitrary code to be executed within iOS. It would require a lot of trial and error to figure out how to craft appropriate commands.