Message-ID: <KFEMINDBKGBEMHACCJHCMEJPDCAA.brett.moore@security-assessment.com>
From: brett.moore at security-assessment.com (Brett Moore)
Subject: Listbox And Combobox Control Buffer Overflow

========================================================================
= Listbox And Combobox Control Buffer Overflow
=
= MS Bulletin posted: October 15, 2003
= http://www.microsoft.com/technet/security/bulletin/MS03-045.asp
=
= Affected Software: 
= 	Microsoft Windows NT 4.0
= 	Microsoft Windows 2000
= 	Microsoft Windows XP
= 	Microsoft Windows 2003
=
= Public disclosure on October 15, 2003
========================================================================

As past history has shown us, Windows has many buffer overflow resulting
from the mishandling of long file names or path names. This one is no
different.

== Description ==

Sending either a LB_DIR message to a listbox or a CB_DIR message to a 
combobox, specifying a large pathname as the parameter will result in 
the following event log message.

------------------------------------------------------------------------
Event Type:       Error
Event Source:     Service Control Manager
Event Category:   None
Event ID:         7031
Description:
The [application] service terminated unexpectedly.  
------------------------------------------------------------------------

The LB_DIR and CB_DIR messages are defined as;

LB_DIR 
  An application sends an LB_DIR message to add a list of filenames
  to a list box
 
  wParam = (WPARAM) (UINT) uAttrs;          // file attributes 
  lParam = (LPARAM) (LPCTSTR) lpszFileSpec; // filename address 
  lpszFileSpec 
    Value of lParam. Pointer to the null-terminated string that
    specifies the filename to add to the list

CB_DIR 
  An application sends a CB_DIR message to add a list of filenames
  to the list box of a combo box. 

  wParam = (WPARAM) (UINT) uAttrs;          // file attributes 
  lParam = (LPARAM) (LPCTSTR) lpszFileSpec; // address of filename 
  lpszFileSpec 
    Value of lParam. Pointer to the null-terminated string that
    specifies the filename to add to the list

== Exploitation ==

On Windows 2000, the utility manager runs under the localsystem account
and contains a listbox control that will accept messages from unprivileged
users, allowing for the escalation of privileges to localsystem level.

The following details are based on the exploitation of that listbox.

After sending a message with a large pathname utilman will cause an
exception within a call to wcscpy.

* From MSDN * 
strcpy, wcscpy Copy a string.
    char *strcpy( char *strDestination, const char *strSource );
    wchar_t *wcscpy( wchar_t *strDestination, const wchar_t *strSource );

Parameters 
   strDestination - Destination string 
   strSource - Null-terminated source string 

Remarks
The strcpy function copies strSource, including the terminating null
character, to the location specified by strDestination.
No overflow checking is performed when strings are copied or appended.
* End MSDN * 

The exception occurs at this code location;

77F81E98   mov         dx,word ptr [ecx]
77F81E9B   mov         word ptr [esi],dx   <-- Exception
77F81E9E   inc         esi
77F81E9F   inc         esi
77F81EA0   inc         ecx
77F81EA1   inc         ecx
77F81EA2   test        dx,dx
77F81EA5   jne         77F81E98

At this point ESI has been incremented to much and is now pointing to an
invalid memory location. The registers look like this;

EAX = 007AF6DC EBX = 0000018D
ECX = 007E0924 EDX = 0000FFFF
ESI = 007B0000 EDI = 007E0000
EIP = 77F81E9B ESP = 007AF6AC
EBP = 007AFD6C EFL = 00000286

The area where the pathname has been copied to starts at 0x007AF6F7,
which is higher than ESP, but lower than EBP. The memory starting at EBP
now contains the data passed in the pathname, and any future reference
to EBP will reference this data.

007AFD6C  58 58 58 58 58  XXXXX
007AFD71  58 58 58 58 58  XXXXX
007AFD76  58 58 58 58 58  XXXXX
007AFD7B  58 58 58 58 58  XXXXX
007AFD80  58 58 58 58 58  XXXXX

Because an exception has occurred, and our pathname has overwritten the
exception handlers on the stack, an unhandled exception will occur when
execution flow reaches;

77F8EB6B   mov         ecx,dword ptr [ebp+18h]	<-- EBP points to buffer
77F8EB6E   call        ecx                      <-- We control ECX

At this point EBX points directly into the buffer and by correctly forming
the pathname, execution flow can be directed back into our buffer. 

Standard stack based overflow techniques apply and exploits can be written
for either Unicode or non-Unicode depending on which API is used to send
the original message.

== Solutions ==

- Install the vendor supplied patch.
- Interactive processes should not run under a higher level account.

== Credit ==

Discovered and advised to Microsoft July 14, 2003 by Brett Moore of
Security-Assessment.com

%-) Greetz to all the people I met in Vegas, there are to many to name.
%-) Special mention to all the boys (and girls) from eEye who showed me 
%-) how to party in true Vegas style!!

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