Finding the Module Base Address in C++ for Malware Analysis

 

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When analyzing malware, it's often necessary to locate the base address of a module in memory. This can be a challenging task, especially if the module has been loaded at a randomized address due to address space layout randomization (ASLR). However, with some basic knowledge of C++ and the Windows API, it's possible to write a simple function to find the base address of a module at runtime.

What is a module?

In the context of malware analysis, a module refers to a DLL (Dynamic Link Library) or EXE (Executable) file that has been loaded into memory by a process. Each module has a base address, which is the starting address of the module in memory. This base address can be found by examining the process's memory map.

How to find the base address of a module using C++

To find the base address of a module in C++, we can use the ToolHelp32 library and its associated functions. Here's an example code snippet that shows how to find the base address of a module given its name:

#include <windows.h>
#include <tlhelp32.h>

DWORD GetModuleBaseAddress(DWORD dwProcessId, const char* lpModuleName) {
    MODULEENTRY32 lpModuleEntry = { 0 };
    HANDLE hSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPMODULE, dwProcessId);

    if (hSnapshot == INVALID_HANDLE_VALUE)
        return NULL;

    lpModuleEntry.dwSize = sizeof(lpModuleEntry);

    if (!Module32First(hSnapshot, &lpModuleEntry)) {
        CloseHandle(hSnapshot);
        return NULL;
    }

    do {
        if (strcmp(lpModuleEntry.szModule, lpModuleName) == 0) {
            CloseHandle(hSnapshot);
            return (DWORD)lpModuleEntry.modBaseAddr;
        }
    } while (Module32Next(hSnapshot, &lpModuleEntry));

    CloseHandle(hSnapshot);
    return NULL;
}

int main() {
    DWORD processId = GetCurrentProcessId();
    const char* moduleName = "kernel32.dll";
    DWORD baseAddress = GetModuleBaseAddress(processId, moduleName);

    if (baseAddress == NULL) {
        printf("Could not find module '%s'\n", moduleName);
    } else {
        printf("Module '%s' found at base address 0x%08X\n", moduleName, baseAddress);
    }

    return 0;
}
 

This code defines a function called GetModuleBaseAddress that takes the process ID and module name as parameters and returns the module base address. In the main function, we get the current process ID and module name, and then call the GetModuleBaseAddress function to find the base address of the module.

How to navigate through the module list

The CreateToolhelp32Snapshot function creates a snapshot of the specified process and its associated modules. The Module32First function retrieves information about the first module in the module list of the specified process. The Module32Next function retrieves information about the next module in the module list.

By using these functions in combination, we can loop through the list of modules and find the one with the specified name.

How to obtain a list of modules for a specified process

To obtain a list of modules for a specified process in malware analysis, we can use the CreateToolhelp32Snapshot function with the TH32CS_SNAPMODULE flag. This creates a snapshot of the specified process and its associated modules. We can then use the Module32First and Module32Next functions to loop through the list of modules and get their information.

Here is an example C++ code that demonstrates how to get the module list for a process:

#include <windows.h>
#include <tlhelp32.h>
#include <iostream>

void printModuleList(DWORD processId)
{
    HANDLE hModuleSnap = INVALID_HANDLE_VALUE;
    MODULEENTRY32 me32;
    hModuleSnap = CreateToolhelp32Snapshot(TH32CS_SNAPMODULE, processId);
    if (hModuleSnap == INVALID_HANDLE_VALUE)
    {
        std::cerr << "CreateToolhelp32Snapshot failed with error code: " << GetLastError() << std::endl;
        return;
    }
    me32.dwSize = sizeof(MODULEENTRY32);
    if (!Module32First(hModuleSnap, &me32))
    {
        std::cerr << "Module32First failed with error code: " << GetLastError() << std::endl;
        CloseHandle(hModuleSnap);
        return;
    }
    std::cout << "Module list for process " << processId << ":" << std::endl;
    do
    {
        std::cout << me32.szModule << " (base address: 0x" << std::hex << (DWORD_PTR)me32.modBaseAddr << ")" << std::endl;
    } while (Module32Next(hModuleSnap, &me32));
    CloseHandle(hModuleSnap);
}

int main()
{
    DWORD processId = GetCurrentProcessId();
    printModuleList(processId);
    return 0;
}

Final Thoughts

The printModuleList function takes the process ID as a parameter and prints out the name and base address of each module in the process. The GetCurrentProcessId function is used to get the ID of the current process. By using this code, you can get a list of modules loaded into a process, which can be useful for identifying malicious code and analyzing its behavior.