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OpenRCE Anti Reverse Engineering Technique >> OllyDbg Memory Breakpoint Detection

Technique Name Category Analysis By Download Added On Last Updated
OllyDbg Memory Breakpoint Detection Debugging ap0x OllyPageGuard.zip March 11 2006
Description:
    .386
      .model flat, stdcall
      option casemap :none   ; case sensitive

      include \masm32\include\windows.inc
      include \masm32\include\user32.inc
      include \masm32\include\kernel32.inc

      includelib \masm32\lib\user32.lib
      includelib \masm32\lib\kernel32.lib

    .data
Alloc dd ?
OLDProtect dd 02040001h
msgTitle db "Execution status:",0h
msgText1 db "No debugger detected!",0h
msgText2 db "Debugger detected!",0h
    .code

start:

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

; The idea is simple. OllyDBG interprets PAGE_GUARD as a
; Memory break-point. If we set SEH and execute PAGE_GUARDed
; code exception will occure. If debugger is present it
; will execute MemBpx and continue executing code after it.
; If debugger is not present handleing will be forwarded to SEH.

; Setup SEH

ASSUME FS:NOTHING
PUSH offset @Check
PUSH FS:[0]
MOV FS:[0],ESP

; Allocate new space

PUSH PAGE_READWRITE
PUSH MEM_COMMIT
PUSH 10000h
PUSH 0
CALL VirtualAlloc

; Write RET there
MOV BYTE PTR[EAX],0C3h
MOV DWORD PTR[Alloc],EAX

; Place Memory break-point
PUSH offset OLDProtect
PUSH PAGE_EXECUTE_READ OR PAGE_GUARD
PUSH 00000010h
PUSH EAX
CALL VirtualProtect

; Execute
CALL [Alloc]

PUSH 30h
PUSH offset msgTitle
PUSH offset msgText2
PUSH 0
CALL MessageBox

PUSH 0
CALL ExitProcess

; SEH handler
@Check:
POP FS:[0]
ADD ESP,4

PUSH 40h
PUSH offset msgTitle
PUSH offset msgText1
PUSH 0
CALL MessageBox

PUSH 0
CALL ExitProcess

end start

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