It would appear that some of Apple’s iPhone source code has been leaked online. According to a number of reports, source code from Apple’s iOS 9 has turned up on GitHub.
The iOS source code is apparently from iOS 9 and the code is apparently for iBoot and according to Motherboard the code is the real deal.
As the code is from iOS 9 it is not exactly relevant to the current release of iOS 11.2.5, but there could be some code in there that is still present in the latest release of Apple’s iOS.
Apparently there are some files missing from the code that has been released on Github so the code cannot be compiled. It could be used by hackers to find vulnerabilities in Apple’s iOS. This could be used for things like jailbreaks. The leaked code also apparently comes with some documents related to iBoot.
Apple has kept iBoot secret in the past even when it has release some source code for iOS and macOS, so they will not be happy about this leaked code.