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Re: Microsoft Windows LoadImage API Integer Buffer overflow
From: Brett Glass <brett () lariat org>
Date: Fri, 24 Dec 2004 17:18:56 -0700

Since it's highly unlikely that Microsoft will handle this bug in a timely manner,
and highly likely that malicious parties will do so over the Christmas weekend,
does anyone know how best to write a shim to defuse this vulnerability?


At 07:58 AM 12/23/2004, flashsky fangxing wrote:

[Security Advisory]
Advisory: [AD_LAB-04004]Microsoft Windows LoadImage API Integer Buffer overflow
Class: Boundary Condition Error
Remote: Yes

Windows NT 
Windows 2000 SP0
Windows 2000 SP1
Windows 2000 SP2
Windows 2000 SP3
Windows 2000 SP4
Windows XP SP0
Windows XP SP1
Windows 2003
not vulnerable:
No one knows:P


An exploitable integer buffer overflow exists in the LoadImage API of the USER32 Lib. This
function loads an icon, a cursor or a bitmap and then try to proceed the image. If an attacker
sends a specially crafter bmp, cur, ico or ani file within an HTML page or in an Email, it is
then possible to run arbitrary code on the affected system.


When the LoadImage API try to proceed the image, it directly uses the size field in the image 
file and then add 4. So if we set the size of image between 0xfffffffc-0xffffffff, an integer buffer
overflow occurs. 

The function defines:

HANDLE LoadImage(
 HINSTANCE hinst,   // handle of the instance containing the image
 LPCTSTR lpszName,  // name or identifier of the image
 UINT uType,        // type of image
 int cxDesired,     // desired width
 int cyDesired,     // desired height
 UINT fuLoad        // load flags

lpszName is the handle to the image to load, uType specifies the type of image to be loaded. 
This parameter can be one of the following values:
IMAGE_BITMAP Loads a bitmap. 
IMAGE_CURSOR Loads a cursor. 
IMAGE_ICON Loads an icon. 

When LoadImage API try to parse the bmp,cur,ico,ani file format, it doesn't implement any check
on the size field and add 4. Look at the code below:

   When use ANI or CUR:
      .text:77D56178                 mov     eax, [ebx+8]                   //Direct read our size here:P
.text:77D5617B                 mov     [ebp+dwResSize], eax         
.text:77D5617E                 jnz     short loc_77D56184
.text:77D56180                 add     [ebp+dwResSize], 4             //add 4 int overflow...
.text:77D56184 loc_77D56184:                           ; CODE XREF: sub_77D5608F+EFj
.text:77D56184                 push    [ebp+dwResSize]                 //allocate a wrong size
.text:77D56187                 push    0
.text:77D56189                 push    dword_77D5F1A0
.text:77D5618F                 call    ds:RtlAllocateHeap

     Then use the fake size for memmov and lead the heap overflow:
      .text:77D561A9                 mov     ecx, [ebx+8]
.text:77D561AC                 mov     esi, [ebx+0Ch]
.text:77D561AF                 add     esi, [ebp+arg_0]
.text:77D561B2                 mov     edx, ecx
.text:77D561B4                 shr     ecx, 2
.text:77D561B7                 mov     edi, eax
.text:77D561B9                 rep movsd
.text:77D561BB                 mov     ecx, edx
.text:77D561BD                 and     ecx, 3
.text:77D561C0                 rep movsb

 More details and POC at http://www.xfocus.net/flashsky/icoExp/index.html


Flashsky(fangxing () venustech com cn;flashsky () xfocus org) discovery this vuln:)
Vulnerability analysis and advisory by Flashsky and icbm.
Special thanks to "Fengshou" project members and all Venustech AD-Lab guys:P


The information in this bulletin is provided "AS IS" without warranty of any
kind. In no event shall we be liable for any damages whatsoever including direct,
indirect, incidental, consequential, loss of business profits or special damages. 

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