What is Process Injection?

It is a method of executing arbitrary code in the address space of a separate live process. Running code in the context of another process may allow access to the process’s memory, system/network resources, and possibly elevated privileges. Execution via process injection may also evade detection from security products since the execution is masked under a legitimate process.

TECHNICAL DETAILS

Open process with Access Rights
LPTHREAD_START_ROUTINE (its a pointer to the application-defined function of type LPTHREAD_START_ROUTINE to be executed by the thread and represents the starting address of the thread in the remote process. The function must exist in the remote process.)
VirtualAllocEx (used to allocate space from the target process virtual memory)
WriteProcessMemory (used to write the path of the shellcode into the allocated memory)
CreateRemoteThread (used to creates a thread in the virtual memory area of a process)
WaitForSingleObject (Waits until the specified object is in the signaled state or the time-out interval elapses)

RtlSetProcessIsCritical used to protect the process from termination , any attempt to terminate the process will cause the windows to crash (Not Stable)