The source code for the part of Apple's iOS operating system that starts at power-up and verifies and loads the rest of the kernel leaked some time last year and was even available on GitHub for a time. Apple asserted its ownership and got GitHub to remove the code, thus ensuring that black hats will give it close attention and circulate it widely, while white hats who don't already have a copy will not be able to copy it legally.
“Key iPhone Source Code Gets Posted Online in ‘Biggest Leak in History’”
Lorenzo Franceschi-Bicchierai, Motherboard, February 8, 2018
This means that tethered jailbreaks, which require the phone to be connected to a computer when booting, could soon be back. These jailbreaks used to be relatively easy to pull off and were common, but are now extremely hard to come by on up-to-date iOS devices, which have advanced security mechanisms. …
It's these security improvements that have effectively killed the once popular jailbreak community. Nowadays, finding bugs and vulnerabilities in iOS is something that requires a significant amount of time and resources, making the result exploits incredibly valuable. That's why the jailbreaking community gets excited for any leak of source code or any exploit that gets released publicly.