Add payload DLL

Executes a MessageBox on DLL_PROCESS_ATTACH to confirm code execution inside the target process.

MyDll.c

@@ -0,0 +1,24 @@
+// MyDll.c
+// Payload DLL for the process injection PoC.
+//
+// DllMain is the entry point called automatically by Windows when the DLL
+// is loaded into a process. On DLL_PROCESS_ATTACH we show a message box
+// as visible proof that code execution was achieved inside the target process.
+
+#include <windows.h>
+
+BOOL APIENTRY DllMain(HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved)
+{
+    if (ul_reason_for_call == DLL_PROCESS_ATTACH)
+    {
+        // MB_TOPMOST | MB_SETFOREGROUND forces the popup to the front,
+        // otherwise it may appear hidden behind other windows.
+        MessageBoxA(
+            GetForegroundWindow(),
+            "DLL injected successfully!\nRunning inside the target process.",
+            "Process Injection PoC",
+            MB_OK | MB_TOPMOST | MB_SETFOREGROUND
+        );
+    }
+    return TRUE;
+}