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Changing ASM Code with a DLL Injection
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GRPsuper9
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PostPosted: Thu Jan 01, 2009 4:43 pm    Post subject: Changing ASM Code with a DLL Injection Reply with quote
Hey guys, im fairly new to Visual C++ so dont flame please Smile.

Ive been looking at this code recently:
Code:
#include <windows.h>

bool bWantsExit;
int *iTime = (int*)0x0100579C;

DWORD WINAPI MyThread()
{
   while( !bWantsExit )
   {
      *iTime = 0;
      Sleep( 10 );
   }
   return 0;
}

BOOL APIENTRY DllMain(HMODULE hModule, DWORD dwMsg, LPVOID lpReserved)
{
   switch( dwMsg )
   {
   case DLL_PROCESS_ATTACH:
      DisableThreadLibraryCalls( hModule );
      bWantsExit = false;
      CreateThread( NULL, 0, (LPTHREAD_START_ROUTINE)MyThread, NULL, 0, 0 );
      return TRUE;
   case DLL_PROCESS_DETACH:
      bWantsExit = true;
      return TRUE;
   }
   return TRUE;
}

Which is meant for Minesweeper. I made a simple little program with Visual Basic 6, that whenever you click a command button, the number in the label goes down by 1. I know the basics of setting a variable right when the DLL is injected (through the code listed above), but how would I make it so my DLL would change the ASM code of the process, lets say from
Code:
sub dx,1
to
Code:
add dx,2
(which is located in address 00401c24)

Im just thinking out loud here, but would this be a codecave? Have it jump from its original code to the modified code then back to the step after 00401c24?

I will upload my "InjectMe.exe" on here, please feel free to scan it with your personal antivirus/antispyware along with this online scanner:
virusscan.jotti.org.

Here are the results from the exe scan I performed:
MD5: 17635dda99f862aa3bd9e7858a083bdf
A-Squared
Found nothing
AntiVir
Found nothing
ArcaVir
Found nothing
Avast
Found nothing
AVG Antivirus
Found nothing
BitDefender
Found nothing
ClamAV
Found nothing
CPsecure
Found nothing
Dr.Web
Found nothing
F-Prot Antivirus
Found nothing
F-Secure Anti-Virus
Found nothing
G DATA
Found nothing
Ikarus
Found nothing
Kaspersky Anti-Virus
Found nothing
NOD32
Found nothing
Norman Virus Control
Found nothing
Panda Antivirus
Found nothing
Sophos Antivirus
Found nothing
VirusBuster
Found nothing
VBA32
Found nothing

The Extension 'zip' was deactivated by an board admin, therefore this Attachment is not displayed.


Last edited by GRPsuper9 on Thu Jan 01, 2009 4:59 pm; edited 1 time in total
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hcavolsdsadgadsg
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PostPosted: Thu Jan 01, 2009 4:58 pm    Post subject: Reply with quote
just write it as expected, it's just bytes that makes up the opcodes.

sub dx, 1 = 66 83 EA 01
add dx, 2 = 66 83 C2 02

use pointers, like you're already doing, or you can try memset.
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GRPsuper9
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PostPosted: Thu Jan 01, 2009 5:04 pm    Post subject: Reply with quote
slovach wrote:
just write it as expected, it's just bytes that makes up the opcodes.

sub dx, 1 = 66 83 EA 01
add dx, 2 = 66 83 C2 02

use pointers, like you're already doing, or you can try memset.

I dont know how to write it as expected though Confused. And instead of setting a value, like I have in the minesweeper example, how would I set the asm code? And just as an fyi, that code is not mine, I didn't write it, I just took it, and learned what I could from it.
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&Vage
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PostPosted: Thu Jan 01, 2009 5:30 pm    Post subject: Reply with quote
Code:

*(WORD*)0x00401c24 ^= 0x0328;
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GRPsuper9
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PostPosted: Thu Jan 01, 2009 5:38 pm    Post subject: Reply with quote
_void_ wrote:
Code:

*(WORD*)0x00401c24 ^= 0x0328;

Thanks. Now where exactly would I put this in my code?
Code:

#include <windows.h>

BOOL APIENTRY DllMain(HMODULE hModule, DWORD dwMsg, LPVOID lpReserved)
{
   switch( dwMsg )
   {
   case DLL_PROCESS_ATTACH:
      *(WORD*)0x00401c24 ^= 0x0328;
      return TRUE;
   }
   return TRUE;
}


And what does 0328 mean? And instead of typing hex, could I possibly use
Code:
add dx,2
instead of the 0x0328?

And may I also ask what the "^" means in *(WORD*)0x00401c24 ^= 0x0328;?

Dont flame, im new Very Happy
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hcavolsdsadgadsg
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PostPosted: Thu Jan 01, 2009 6:24 pm    Post subject: Reply with quote
http://www.cplusplus.com/doc/tutorial/pointers.html
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&Vage
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PostPosted: Thu Jan 01, 2009 6:32 pm    Post subject: Reply with quote
^ = xor
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GRPsuper9
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PostPosted: Thu Jan 01, 2009 6:47 pm    Post subject: Reply with quote
I dont quite understand how I would change the opcodes of the address with that website. From your own perspective, which method would be easier and better to use? Pointer Method or Memset?

EDIT:
Ive looked at memset also, but I still dont understand it. Could you write an example for me to learn off of? This is the first time I've ever coded with C++.
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hcavolsdsadgadsg
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PostPosted: Thu Jan 01, 2009 7:15 pm    Post subject: Reply with quote
i meant memcpy actually, oops.

read the site i linked.

example with pointers.

step through it in the debugger, and check the address that HeapAlloc returns, and it will become clear.

Code:
#include <Windows.h>
#include <iostream>

int main ()
{
   byte numbers[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
   byte* p;

   p = numbers;

   //allocate 8 bytes of memory
   void* offset = (void*)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 8);

   offset = p;

   HeapFree(GetProcessHeap(), 0, offset);   
   return 0;
}
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GRPsuper9
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PostPosted: Thu Jan 01, 2009 7:40 pm    Post subject: Reply with quote
slovach wrote:
i meant memcpy actually, oops.

read the site i linked.

example with pointers.

step through it in the debugger, and check the address that HeapAlloc returns, and it will become clear.

Code:
#include <Windows.h>
#include <iostream>

int main ()
{
   byte numbers[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
   byte* p;

   p = numbers;

   //allocate 8 bytes of memory
   void* offset = (void*)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 8);

   offset = p;

   HeapFree(GetProcessHeap(), 0, offset);   
   return 0;
}

Your main function is int main. How would it work through a dll? Im really confused Crying or Very sad. When I tried to build it in order to debug it, it gave me an error saying it failed or something.
But im guessing
Code:
void* offset = (void*)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 8);
Assigns the current address to GetProcessHeap and then
Code:
HeapFree(GetProcessHeap(), 0, offset);
nulls it? Although if im right about it nulling it, I dont understand how I would replace it with something I want.
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hcavolsdsadgadsg
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PostPosted: Thu Jan 01, 2009 8:09 pm    Post subject: Reply with quote
it was an example of using pointers, and how you can accomplish what you want with them.

http://msdn.microsoft.com/en-us/library/aa366597(VS.85).aspx

Quote:
If the function succeeds, the return value is a pointer to the allocated memory block.


http://msdn.microsoft.com/en-us/library/aa366701(VS.85).aspx


I'm allocating some memory (8 bytes worth, and setting them all to 0) so I have to place to use in my example... but you already have a place to work with. HINT HINT NUDGE NUDGE
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GRPsuper9
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PostPosted: Thu Jan 01, 2009 9:10 pm    Post subject: Reply with quote
Honestly, im still very confused haha. Its kind of complicated to learn it by yourself when you've never really had any experience with the language.
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hcavolsdsadgadsg
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PostPosted: Thu Jan 01, 2009 10:10 pm    Post subject: Reply with quote
which is exactly why you should go to the link I posted, and start reading.

http://www.cplusplus.com/doc/tutorial/
http://www.cplusplus.com/doc/tutorial/pointers.html
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GRPsuper9
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PostPosted: Thu Jan 01, 2009 10:17 pm    Post subject: Reply with quote
I dont see anything on those sites that deal with changing the actual asm code, just changing the value of a pointer, which is not what I want at all. If im wrong, let me know and let me know where in those sites to look.

All I read about was about different kinds of pointers and how to assign values onto them and use them in mathematical equations.
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lurc
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PostPosted: Thu Jan 01, 2009 10:39 pm    Post subject: Reply with quote
What you need is not how to modify the memory of another process, but HOW TO PROGRAM IN C++. There is no fucking point in learning only a certain aspect of programming, especially a more difficult aspect, if you're to stubborn to learn the basics.

So go read what slovach posted, take some time to get used to the language, learn.
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