Enhancing Software with Microsoft Detours: A Deep Dive

Microsoft Detours is an instrumental library for developers working on Windows, enabling the interception and modification of binary functions. This article will explore how Detours can revolutionize software development, debugging, and security, with a focus on practical coding examples.

Understanding Microsoft Detours

What is Microsoft Detours?

Detours is a library that allows for the interception of Win32 functions by rewriting target function images at runtime. This capability is crucial for:

• Software Debugging: To trace function calls or modify function behavior without altering the source code.
• Security Enhancements: By monitoring or altering system calls to enhance security protocols.
• Reverse Engineering: To understand or alter the behavior of compiled programs.

Core Components

It is made up of three core components:

• Detours: The mechanism to redirect function calls.
• Trampolines: Code snippets that allow the original function to be called after detour logic.
• Payload Functions: Custom functions where the new logic resides.

Setting Up a Simple Detour

Here’s how you might set up a detour in C++:

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

// Original function
static int (WINAPI * TrueMessageBox)(HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType) = MessageBoxW;

// Detour function
int WINAPI MyMessageBox(HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType) {
    std::cout << "MessageBox intercepted!" << std::endl;
    return TrueMessageBox(hWnd, L"Intercepted!", lpCaption, uType);
}

int main() {
    DetourTransactionBegin();
    DetourUpdateThread(GetCurrentThread());
    DetourAttach(&(PVOID&)TrueMessageBox, MyMessageBox);
    DetourTransactionCommit();

    MessageBoxW(NULL, L"Will this be intercepted?", L"Test", MB_OK);

    DetourTransactionBegin();
    DetourUpdateThread(GetCurrentThread());
    DetourDetach(&(PVOID&)TrueMessageBox, MyMessageBox);
    DetourTransactionCommit();

    return 0;
}

This example demonstrates how to intercept MessageBoxW, modify its behavior, and then restore the original function.

Implementation Strategies

Identifying Targets

Use tools like IDA Pro or Ghidra to analyze which functions to detour. Look for functions that are critical for your debugging or security needs.

Creating and Managing Detours

• Dynamic Linking: Use DetourAttach and DetourDetach for runtime modifications.
• Performance: Always consider the performance hit. Use profiling tools to measure impact.

Monitoring File Operations

#include <windows.h>
#include <detours.h>
#include <fstream>

static HANDLE (WINAPI * RealCreateFile)(LPCTSTR lpFileName, DWORD dwDesiredAccess, DWORD dwShareMode, LPSECURITY_ATTRIBUTES lpSecurityAttributes, DWORD dwCreationDisposition, DWORD dwFlagsAndAttributes, HANDLE hTemplateFile) = CreateFile;

HANDLE WINAPI MyCreateFile(LPCTSTR lpFileName, DWORD dwDesiredAccess, DWORD dwShareMode, LPSECURITY_ATTRIBUTES lpSecurityAttributes, DWORD dwCreationDisposition, DWORD dwFlagsAndAttributes, HANDLE hTemplateFile) {
    std::ofstream log("file_access.log", std::ios_base::app);
    log << "File accessed: " << lpFileName << std::endl;
    return RealCreateFile(lpFileName, dwDesiredAccess, dwShareMode, lpSecurityAttributes, dwCreationDisposition, dwFlagsAndAttributes, hTemplateFile);
}

void SetupFileMonitoring() {
    DetourTransactionBegin();
    DetourUpdateThread(GetCurrentThread());
    DetourAttach(&(PVOID&)RealCreateFile, MyCreateFile);
    DetourTransactionCommit();
}

This snippet logs all file access attempts, showcasing how Detours can be used for security monitoring.

Performance Considerations

• Selective Interception: Only detour functions where necessary.
• Optimize Payloads: Keep the logic in payload functions lean to minimize overhead.

Conclusion

Microsoft Detours provides a powerful way to extend or alter software functionality at runtime, offering immense value in debugging, security, and reverse engineering. By understanding its architecture and implementing it with care for performance, developers can unlock new possibilities in software manipulation. Remember, with great power comes the responsibility to optimize for efficiency and security.