Insecure IPC — XPC & Mach Ports

On Apple platforms, the most interesting trust boundary is not the network — it is the gap between two processes on the same device. XPC and Mach ports are how those processes talk, and a privileged service that acts on a message without checking who sent it is the classic local privilege-escalation bug. This walks the message model, where the boundary actually sits, how to inspect a service on an app you own, and how peer validation shuts the hole.