💉 DLL-MessageBox-Hook (x64)

A simple Windows x64 DLL hook demo that intercepts calls to MessageBoxA using inline patching (manual trampoline).
Perfect for understanding DLL injection, function hooking, and runtime behavior modification.

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🧩 Features

• Hooks MessageBoxA via mov rax / jmp rax (12-byte patch, x64-compliant)
• Displays a custom message (💥 p0wn3d!) when the app calls MessageBoxA
• Can be injected into any x64 Win32 app calling MessageBoxA
• Includes a test app with a button that triggers a MessageBox

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🛠️ Build

🧪 DLL

Compile the DLL from hook64_msgboxa.c:

cl /LD hook64_msgboxa.c /Fehook64_msgboxa.dll user32.lib

⚠️ Requires Visual Studio + Developer Command Prompt for x64

🧪 Demo App (x64)

Compile simple_app.c:

cl simple_app.c /Fesimple_app.exe user32.lib gdi32.lib

The app shows a window with a button. Clicking it triggers MessageBoxA.

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🚀 Usage

• Start simple_app.exe
• Use a DLL injector (Python or C) to inject hook64_msgboxa.dll
• Click the button in the window

✅ You’ll see:

Intercepted
💥 p0wn3d!

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🧠 How it works

• Finds MessageBoxA in user32.dll
• Saves its first 12 bytes
• Overwrites it with:

mov rax, HookedFunction
jmp rax

• Redirects execution to HookedMessageBoxA, which modifies the message
• Optionally, the hook can be removed before calling the original

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🛡️ Notes

• This only works on x64 processes
• Hooking x86 requires a different approach (jmp rel32, 5 bytes)
• Modern apps often use MessageBoxW (Unicode); hook that if needed

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