Microsoft Windows LoadImage API Integer Buffer overflow Dec 23 2004 02:58PM
flashsky fangxing (flashsky xfocus org) (1 replies)

[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 (at) venustech.com (dot) cn [email concealed];flashsky (at) xfocus (dot) org [email concealed]) 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.

Copyright 1996-2004 VENUSTECH. All Rights Reserved. Terms of use.

VENUSTECH Security Lab



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[ reply ]
Re: Microsoft Windows LoadImage API Integer Buffer overflow Dec 25 2004 12:18AM
Brett Glass (brett lariat org)


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