110 lines
1.5 KiB
NASM
110 lines
1.5 KiB
NASM
format binary
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use32
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include 'std.inc'
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; On entrance to each shellcode segment the ebx register will be a vtable of std funcs
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; printf
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; puts
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; scanf
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; sin
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; cos
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; tan
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; asin
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; acos
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; atan
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; malloc
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; free
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; esi contains the base address of the shellcode segment
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; edi contains the address of the part of the flag that this segment fills
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; edx contains the number of the block
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jmp start
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startup_text db 'What did you say?',0
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start:
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push edi
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lea ecx, [esi+startup_text]
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push ecx
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lea eax, [ebx + 0x4]
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mov eax, dword [eax]
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call dword [eax]
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pop ebp
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xor eax, eax
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push eax
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push eax
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mov eax, esp
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push eax
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lea eax, [ebx + 8]
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mov eax, dword [eax]
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lea ecx, [esi+scanf_text]
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push ecx
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call dword [eax]
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add esp, 8
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pop ecx
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pop eax
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pop edi
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mov dword [edi], ecx
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lea edx, [esi+to_match]
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.check:
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movzx ecx, byte [edi]
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call check_char
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cmp eax, 0
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jz idiot
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inc edi
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inc edx
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cmp byte [edx], 0
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jnz .check
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ret
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scanf_text db '%4[^',ENDL,']'
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; ecx = input'd char
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; edx = ptr to char to match
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check_char:
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cmp ecx, CHAR_a ; 97
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jl fail
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cmp ecx, 126
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jge fail
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sub ecx, CHAR_a ; 97
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add ecx, esi
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lea ecx, [ecx + alphabet]
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movzx eax, byte [ecx]
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cmp byte [edx], al
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jnz fail
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mov eax, 1
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ret
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idiot_text db 'Wrong...', 0
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fail:
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mov eax, 0
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ret
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to_match db 'xtnq', 0
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idiot:
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lea ecx, [esi+idiot_text]
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push ecx
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lea eax, [ebx + 0x4]
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mov eax, dword [eax]
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call dword [eax]
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pop ebp
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dec esp
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ret
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alphabet db 'hqxfbntvirwml{cap|z}sjeodygku', 0
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; abcdefghijklmnopqrstuvwxyz{|}
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; flag is "cgfb"
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resv_stuff 512-$
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