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OpenRCE Anti Reverse Engineering Technique >> Ring3 Debugger Detection via LDR_MODULE

Technique Name Category Analysis By Download Added On Last Updated
Ring3 Debugger Detection via LDR_MODULE Debugging ap0x March 17 2006 March 18 2006
Description:
; #########################################################################

      .586
      .model flat, stdcall
      option casemap :none   ; case sensitive

; #########################################################################
      include \masm32\include\windows.inc
      include \masm32\include\user32.inc
      include \masm32\include\kernel32.inc
      include \masm32\include\comdlg32.inc
      
      includelib \masm32\lib\user32.lib
      includelib \masm32\lib\kernel32.lib
      includelib \masm32\lib\comdlg32.lib
      
; #########################################################################  
    .data
DbgFoundTitle db "Debugger found:",0h
DbgFoundText db "Debugger has been found!",0h
DbgNotFoundTitle db "Debugger not found:",0h
DbgNotFoundText db "Debugger not found!",0h
Tries db 30
Alloc dd ?
    .code

start:

; MASM32 antiRing3Debugger example
; coded by ap0x
; Reversing Labs: http://ap0x.headcoders.net

ASSUME FS:NOTHING
PUSH offset _SehExit
PUSH DWORD PTR FS:[0]
MOV FS:[0],ESP

; Get NtGlobalFlag

MOV EAX,DWORD PTR FS:[30h]

; Get LDR_MODULE

MOV EAX,DWORD PTR[EAX+12]

; The trick is here ;) If ring3 debugger is present memory will be allocated
; and it will contain 0xFEEEFEEE bytes at the end of alloc. This will only
; happen if ring3 debugger is present!
; If there is no debugger SEH will fire and take control.

; Note: This code works only on NT systems!

_loop:
INC EAX
CMP DWORD PTR[EAX],0FEEEFEEEh
JNE _loop
DEC [Tries]
JNE _loop

PUSH 30h
PUSH offset DbgFoundTitle
PUSH offset DbgFoundText
PUSH 0
CALL MessageBox
PUSH 0
CALL ExitProcess
RET
_Exit:
PUSH 40h
PUSH offset DbgNotFoundTitle
PUSH offset DbgNotFoundText
PUSH 0
CALL MessageBox
PUSH 0
CALL ExitProcess
RET

_SehExit:
POP FS:[0]
ADD ESP,4
JMP _Exit

end start

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