Andres Rey - (User32.dll Icon Size Crash)

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Application: User32.dll (Windows 98SE Version (4.10.2222)) (Maybe other
Windows versions too)
Bug: Crash the program that attempts to open the icon
Explotation: Local / Remote*
Author: Andres Rey (andreskrey (at) gmail (dot) com [email concealed])

(* Only sometimes can be used as a remote exploit, see point 5)

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1) Introduction
2) Bug
3) PoC
4) Making the exploit
5) Examples of the Real Life
6) Disclosure

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1) Introduction
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User32.dll Is a core component of the Windows kernel

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2) Bug
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The bug is (probably) in the LoadIconA function of user32.dll. When it reads
a bitmap with the extention .ico and it has a large size (65535x65535), the
dll crash, and the program that called the function gets killed

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2) PoC
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The attached file is a zip with the bitmap/icon compressed. Just decompress
it to a folder and open it (Explorer.exe will crash), or open with any
program that can load a icon (The program will crash)

WARNING!: Don't decompress to the desktop!!, or your explorer.exe will crash
and crash and crash until you delete the icon

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4) Making the exploit
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Just open a bitmap in a hexa editor and modify the width and height data:

Locate the "XXXX" values...

------------------------------------------------------------------------
----
00000000 : 424D 38F9 1500 0000 0000 3600 0000 2800 0000 XXXX
00000010 : 0000 XXXX 0000 0100 1800 0000 0000 02F9 1500 120B
------------------------------------------------------------------------
----

...and change to:

------------------------------------------------------------------------
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00000000 : 424D 38F9 1500 0000 0000 3600 0000 2800 0000 FFFF
00000010 : 0000 FFFF 0000 0100 1800 0000 0000 02F9 1500 120B
------------------------------------------------------------------------
----

Then change the extention to ".ico". Notice that the system will crash. (I
use Total Commander with the icons disabled to manipulate the file)

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5) Examples of the Real Life
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1. Send it through IM
2. Set it as "favicon" of the web pages (<--- Remote version)
3. Put in the desktop of the victim to crash the system everytime
it starts
4. Etc.

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7) Disclosure
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Microsoft wasn't notified
(Don't know the bugs mail!, it's askbill (at) microsoft (dot) com [email concealed]?)

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That's all, hope you found it usefull

Andres Rey
andreskrey (at) gmail (dot) com [email concealed]

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