HadesGate

A New Method Of Retrieving System Call Service Numbers By Parsing NtOsKrnl Exports.

How Does It Work?

If we open ntoskrnl.exe in IDA, And search for functions with the Zw prefix and select a random one, For example ZwAlpcCreatePort, We will find this:

public ZwAlpcCreatePort
ZwAlpcCreatePort proc near
mov     rax, rsp
cli
sub     rsp, 10h
push    rax
pushfq
push    10h
lea     rax, nullsub_4
push    rax
mov     eax, 7Bh <--- This is the SSN
jmp     sub_140411580
ZwAlpcCreatePort endp

So what HadesGate does is parse the exports, Look for functions with the Zw prefix, Go through the stub's memory until we find a 0xB8 opcode in the stub, Which indicates we are currently going through the mov eax, SSN line, Then HadesGate extracts the SSN from the function and returns.

Problems With It

This method will NOT get you every single SSN you want, So I wouldn't suggest using it in a real engagement unless the system calls you need are exported in ntoskrnl.exe.