有时候我们需要对其它应用程序发送和接收的网络数据进行拦截,比如要对IE发送的HTTP头进行分析,得到请求的地址等.这次我们可以用一些例如WPE, Sniffer之类的工具来达到目的.但是工具功能有限,要想实现更强大的功能,还是我们自己动手来DIY吧.

拦截网络数据封包的方法有三种,一是将网卡设为混杂模式,这次就可以监视到局域网上所有的数据包,二是HOOK目标进程的发送和接收的API函数,第三种方法是自己实现一个代理的DLL.在这里我们使用HOOK API的方法,这样易于实现,而且也不会得到大量的无用数据(如第一种方法就会监视到所有的网络数据).

下面是一个尽量简化了的API HOOK的模版,原理是利用消息钩子将DLL中的代码注入到目标进程中,再用GetProcAddress得到API函数入口地址,将函数入口址改为自己定义的函数入口,这样就得到了API函数的相应参数,处理完后,再改回真实API函数入口地址,并调用它.

HOOK.DLL的代码:
library Hook;

uses
  SysUtils,
  windows,
  Messages,
  APIHook in ´APIHook.pas´;

type
  PData = ^TData;
  TData = record
    Hook: THandle;
    Hooked: Boolean;
  end;
 
var
  DLLData: PData;

{------------------------------------}
{过程名:HookProc
{过程功能:HOOK过程
{过程参数:nCode, wParam, lParam消息的相
{         关参数
{------------------------------------}
procedure HookProc(nCode, wParam, lParam: LongWORD);stdcall;
begin
  if not DLLData^.Hooked then
  begin
    HookAPI;
    DLLData^.Hooked := True;
  end;
  //调用下一个Hook
  CallNextHookEx(DLLData^.Hook, nCode, wParam, lParam);
end;

{------------------------------------}
{函数名:InstallHook
{函数功能:在指定窗口上安装HOOK
{函数参数:sWindow:要安装HOOK的窗口
{返回值:成功返回TRUE,失败返回FALSE
{------------------------------------}
function InstallHook(SWindow: LongWORD):Boolean;stdcall;
var
  ThreadID: LongWORD;
begin
  Result := False;
  DLLData^.Hook := 0;
  ThreadID := GetWindowThreadProcessId(sWindow, nil);
  //给指定窗口挂上钩子
  DLLData^.Hook := SetWindowsHookEx(WH_GETMESSAGE, @HookProc, Hinstance, ThreadID);
  if DLLData^.Hook > 0 then
    Result := True  //是否成功HOOK
  else
    exit;
end;

{------------------------------------}
{过程名:UnHook
{过程功能:卸载HOOK
{过程参数:无
{------------------------------------}
procedure UnHook;stdcall;
begin
  UnHookAPI;
  //卸载Hook
  UnhookWindowsHookEx(DLLData^.Hook);
end;

{------------------------------------}
{过程名:DLL入口函数
{过程功能:进行DLL初始化,释放等
{过程参数:DLL状态
{------------------------------------}
procedure MyDLLHandler(Reason: Integer);
var
  FHandle: LongWORD;
begin
  case Reason of
    DLL_PROCESS_ATTACH:
    begin            //建立文件映射,以实现DLL中的全局变量
      FHandle := CreateFileMapping($FFFFFFFF, nil, PAGE_READWRITE, 0, $ffff, ´MYDLLDATA´);
      if FHandle = 0 then
      if GetLastError = ERROR_ALREADY_EXISTS then
      begin
        FHandle := OpenFileMapping(FILE_MAP_ALL_ACCESS, False, ´MYDLLDATA´);
        if FHandle = 0 then Exit;
      end else Exit;
      DLLData := MapViewOfFile(FHandle, FILE_MAP_ALL_ACCESS, 0, 0, 0);
      if DLLData = nil then
        CloseHandle(FHandle);
    end;
    DLL_PROCESS_DETACH:
    begin
      if Assigned(DLLData) then
      begin
        UnmapViewOfFile(DLLData);
        DLLData := nil;
      end;
    end;
  end;
end;

{$R *.res}
exports
  InstallHook, UnHook, HookProc;

begin
  DLLProc := @MyDLLHandler;
  MyDLLhandler(DLL_PROCESS_ATTACH);
  DLLData^.Hooked := False;
end.

----------------------------------------------------------------------------------------
APIHook.Pas的代码:

unit APIHook;

interface

uses
  SysUtils,
  Windows, WinSock;

type
  //要HOOK的API函数定义
  TSockProc = function (s: TSocket; var Buf; len, flags: Integer): Integer; stdcall;

  PJmpCode = ^TJmpCode;
  TJmpCode = packed record
    JmpCode: BYTE;
    Address: TSockProc;
    MovEAX: Array [0..2] of BYTE;
  end;

  //--------------------函数声明---------------------------
  procedure HookAPI;
  procedure UnHookAPI;

var
  OldSend, OldRecv: TSockProc;      //原来的API地址
  JmpCode: TJmpCode;
  OldProc: array [0..1] of TJmpCode;
  AddSend, AddRecv: pointer;        //API地址
  TmpJmp: TJmpCode;
  ProcessHandle: THandle;
implementation

{---------------------------------------}
{函数功能:Send函数的HOOK
{函数参数:同Send
{函数返回值:integer
{---------------------------------------}
function MySend(s: TSocket; var Buf; len, flags: Integer): Integer; stdcall;
var
  dwSize: cardinal;
begin
  //这儿进行发送的数据处理
  MessageBeep(1000);           //简单的响一声
  //调用直正的Send函数
  WriteProcessMemory(ProcessHandle, AddSend, @OldProc[0], 8, dwSize);
  Result := OldSend(S, Buf, len, flags);
  JmpCode.Address := @MySend;
  WriteProcessMemory(ProcessHandle, AddSend, @JmpCode, 8, dwSize);
end;

{---------------------------------------}
{函数功能:Recv函数的HOOK
{函数参数:同Recv
{函数返回值:integer
{---------------------------------------}
function MyRecv(s: TSocket; var Buf; len, flags: Integer): Integer; stdcall;
var
  dwSize: cardinal;
begin
  //这儿进行接收的数据处理
  MessageBeep(1000);         //简单的响一声
  //调用直正的Recv函数
  WriteProcessMemory(ProcessHandle, AddRecv, @OldProc[1], 8, dwSize);
  Result := OldRecv(S, Buf, len, flags);
  JmpCode.Address := @MyRecv;
  WriteProcessMemory(ProcessHandle, AddRecv, @JmpCode, 8, dwSize);
end;

{------------------------------------}
{过程功能:HookAPI
{过程参数:无
{------------------------------------}
procedure HookAPI;
var
  DLLModule: THandle;
  dwSize: cardinal;
begin
  ProcessHandle := GetCurrentProcess;
  DLLModule := LoadLibrary(´ws2_32.dll´);       
  AddSend := GetProcAddress(DLLModule, ´send´);  //取得API地址
  AddRecv := GetProcAddress(DLLModule, ´recv´);
  JmpCode.JmpCode := $B8;
  JmpCode.MovEAX[0] := $FF;
  JmpCode.MovEAX[1] := $E0;
  JmpCode.MovEAX[2] := 0;
  ReadProcessMemory(ProcessHandle, AddSend, @OldProc[0], 8, dwSize);
  JmpCode.Address := @MySend;
  WriteProcessMemory(ProcessHandle, AddSend, @JmpCode, 8, dwSize);   //修改Send入口
  ReadProcessMemory(ProcessHandle, AddRecv, @OldProc[1], 8, dwSize);
  JmpCode.Address := @MyRecv;
  WriteProcessMemory(ProcessHandle, AddRecv, @JmpCode, 8, dwSize);   //修改Recv入口
  OldSend := AddSend;
  OldRecv := AddRecv;
end;

{------------------------------------}
{过程功能:取消HOOKAPI
{过程参数:无
{------------------------------------}
procedure UnHookAPI;
var
  dwSize: Cardinal;
begin
  WriteProcessMemory(ProcessHandle, AddSend, @OldProc[0], 8, dwSize);
  WriteProcessMemory(ProcessHandle, AddRecv, @OldProc[1], 8, dwSize);
end;

end.

---------------------------------------------------------------------------------------------
编译这个DLL后,再新建一个程序调用这个DLL的InstallHook并传入目标进程的主窗口句柄就可:
unit fmMain;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
  InstallHook: function (SWindow: THandle):Boolean;stdcall;
  UnHook: procedure;stdcall;
implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  ModuleHandle: THandle;
  TmpWndHandle: THandle;
begin
  TmpWndHandle := 0;
  TmpWndHandle := FindWindow(nil, ´目标窗口的标题´);
  if not isWindow(TmpWndHandle) then
  begin
    MessageBox(self.Handle, ´没有找到窗口´, ´!!!´, MB_OK);
    exit;
  end;
  ModuleHandle := LoadLibrary(´Hook.dll´);
  @InstallHook := GetProcAddress(ModuleHandle, ´InstallHook´);
  @UnHook := GetProcAddress(ModuleHandle, ´UnHook´);
  if InstallHook(FindWindow(nil, ´Untitled´)) then
    ShowMessage(´Hook OK´);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  UnHook
end;

end.