Earlier this year, I discovered a flaw in XNU, which is the kernel that Apple uses on both macOS and iOS. While it’s not a particularly complicated flaw, I wanted to explain how I discovered it and how it works, both so that I can motivate others and so that they can learn from my discovery. Within the memdev.c file (the ramdisk device driver), I found the source of the vulnerability, which was a write/read operation that exceeded the allowed range. Why are ramdisks such an intriguing target to look at? If you identify a bug in the driver, it may give you the ability to execute code in the kernel. Additionally, on some systems, you may be able to construct ramdisks with particular settings such that it is mapped to physical memory, which may give you the ability to read and write data to physical memory. ...

Mistreatment by Apple Security is unfortunately something you’re likely to come across on a regular basis. Usually this concerns people that conduct free work for Apple in their spare time by auditing their assets. Despite Apple’s website claiming the opposite, you’ll frequently find things like quiet patching, no credit, no bounties, and an appalling lack of communication. This is unwise on Apple’s part because it frustrates people who find these bugs and disincentivizes them from sharing them with Apple. Remember, every bug that gets reported to them (instead of being sold to some shady outfit) and that gets fixed subsequently is one that can not be exploited in the future to make your device less safe. The very least they can do to honour the work of independent researchers is to communicate clearly and give them credit where appropriate. ...