First, you will want to inject a dll in the target process. To do so, you can use this code:
Injector.h
#ifndef INJECTOR_H_INCLUDED
#define INJECTOR_H_INCLUDED
#include <Windows.h>
#include <string>
class Injector
{
public:
/**
* Loads a DLL into the remote process
* @Return true on sucess, false on failure
*/
bool InjectDll(DWORD processId, std::string dllPath);
private:
};
#endif // INJECTOR_H_INCLUDED
Injector.cpp
#include "Injector.h"
bool Injector::InjectDll(DWORD processId, std::string dllPath)
{
HANDLE hThread, hProcess;
void* pLibRemote = 0; // the address (in the remote process) where szLibPath will be copied to;
HMODULE hKernel32 = GetModuleHandle("Kernel32");
HINSTANCE hInst = GetModuleHandle(NULL);
char DllFullPathName[_MAX_PATH];
GetFullPathName(dllPath.c_str(), _MAX_PATH, DllFullPathName, NULL);
// Get process handle
hProcess = OpenProcess(PROCESS_ALL_ACCESS, FALSE, processId);
// copy file path in szLibPath
char szLibPath[_MAX_PATH];
strcpy_s(szLibPath, DllFullPathName);
// 1. Allocate memory in the remote process for szLibPath
pLibRemote = VirtualAllocEx( hProcess, NULL, sizeof(szLibPath), MEM_COMMIT, PAGE_READWRITE );
if (pLibRemote == NULL)
{
// probably because you don't have administrator's right
return false;
}
// 2. Write szLibPath to the allocated memory
WriteProcessMemory(hProcess, pLibRemote, (void*)szLibPath, sizeof(szLibPath), NULL);
// 3. Force remote process to load dll
hThread = CreateRemoteThread(hProcess, NULL, 0, (LPTHREAD_START_ROUTINE) GetProcAddress(hKernel32,"LoadLibraryA"), pLibRemote, 0, NULL);
if (hThread == NULL)
{
return false;
}
return true;
}
main.cpp
#include "Injector.h"
int main()
{
Injector injector;
DWORD processId = 1653; // change the process id here.
if (injector.InjectDll(processId, "injected.dll"))
{
printf("Good job, you injected the dll
");
}
else
{
printf("Something wrong happened
");
}
while (true);
}
Then you have to make your dll. This is where it gets a little more complicated. First some includes:
injected.dll
#include <Windows.h>
#include <stdio.h>
Then we need to make a function that will detour the right location:
void DetourAddress(void* funcPtr, void* hook, BYTE* mem)
{
BYTE cmd[5] = { 0xE9, 0x00, 0x00, 0x00, 0x00 }; // jump place holder
void* RVAaddr = (void*)((DWORD)funcPtr + (DWORD)GetModuleHandle(NULL)); // base + relative address
// make memory readable/writable
DWORD dwProtect;
VirtualProtect(RVAaddr, 5, PAGE_EXECUTE_READWRITE, &dwProtect);
// read memory
ReadProcessMemory(GetCurrentProcess(), (LPVOID)RVAaddr, &mem[2], 5, NULL);
// write jmp in cmd
DWORD offset = ((DWORD)hook - (DWORD)RVAaddr - 5); // (dest address) - (source address) - (jmp size)
memcpy(&cmd[1], &offset, 4); // write address into jmp
WriteProcessMemory(GetCurrentProcess(), (LPVOID)RVAaddr, cmd, 5, 0); // write jmp
// write mem
VirtualProtect(mem, 13, PAGE_EXECUTE_READWRITE, &dwProtect);
void* returnAdress = (void*)((DWORD)RVAaddr + 5);
memcpy(&mem[8], &returnAdress, 4); // write return address into mem
// reprotect
VirtualProtect(RVAaddr, 5, dwProtect, NULL);
}
If you need to remove your dll at some point, you will need to restore the code:
void PatchAddress(void* funcPtr, BYTE* mem)
{
void* RVAaddr = (void*)((DWORD)funcPtr + (DWORD)GetModuleHandle(NULL)); // base + relative address
// make memory readable/writable
DWORD dwProtect;
VirtualProtect(funcPtr, 5, PAGE_EXECUTE_READWRITE, &dwProtect);
WriteProcessMemory(GetCurrentProcess(), (LPVOID)RVAaddr, &mem[2], 5, NULL); // write jmp
VirtualProtect(RVAaddr, 5, dwProtect, NULL);
}
Next, we need to make a function out of the detoured bytes in order for the program to execute them, so that it isn't affected by our detour. Add this in global space:
// memory (0x5E = pop esi, 0x68 = push DWORD, 0xC3 = RETN)
BYTE detourMem[13] = { 0x5E, 0x5E, 0x0, 0x0, 0x0, 0x0, 0x0, 0x68, 0x00, 0x00, 0x00, 0x00, 0xC3 };
// Convert bytes array to function
typedef void ( * pFunc)();
pFunc funcMem = (pFunc) &detourMem;
// I also added a variable as an example of what you can do with it.
DWORD var = 0;
After that, you need your detouring function:
_declspec(naked) void DetourFunction()
{
// we need to push all flag and registers on the stack so we don't modify them by accident
__asm
{
PUSHFD
PUSHAD
// You can do "whatever" you want here in assembly code
// ex, put eax value into var:
mov var, eax
}
printf("this code is executed everytime the detoured function is called
");
// Do whatever you want in c++ here
if (var < 7)
{
// eax was smaller than 7
}
// We pop every flags and registers we first pushed so that the program continue as it was supposed to
__asm
{
// we set everything back to normal
POPAD
POPFD
push esi
// we call our funcMem
mov edx, funcMem;
call edx
}
}
Finaly, here is how your DLLMain would look like:
BOOL APIENTRY DllMain( HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved )
{
DWORD detouredAddress = 0x689B; // add the RELATIVE ADDRESS of the location you want to detour
FILE *stream;
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
// Only add this if you want a console to appears when you inject your dll (don't forget FreeConsole when you remove the dll)
AllocConsole();
freopen_s(&stream, "CONOUT$", "w", stdout);
// If you need to know the base address of the process your injected:
printf("base address: 0x%X
", (DWORD)GetModuleHandle(NULL));
// Our detour function
DetourAddress((void*)detouredAddress, (void*)&DetourFunction, detourMem);
break;
case DLL_PROCESS_DETACH:
// We restore the process to have what it was before it was injected
PatchAddress((void*)detouredAddress, detourMem);
FreeConsole();
break;
}
return true;
}
I understand this is a lot all at once, so if you have any questions don't hesitate!
