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                             Luigi Auriemma

Application:  Unreal engine
              http://www.unrealtechnology.com
Versions:     almost any game which uses the Unreal engine is affected
              by this vulnerability except some like Unreal Tournament
              2004, Dead Man's Hand and possibly other old games
Platforms:    Windows, Linux, Mac
Bug:          format string
Exploitation: remote, versus client
Date:         11 Sep 2008
Author:       Luigi Auriemma
              e-mail: aluigi@autistici.org
              web:    aluigi.org


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1) Introduction
2) Bug
3) The Code
4) Fix


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===============
1) Introduction
===============


The Unreal engine is the game engine developed by Epic Games
(http://www.epicgames.com) and used in many famous commercial games of
which the main example is just the lucky Unreal Tournament series.


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======
2) Bug
======


The Unreal engine is affected by some format string vulnerabilities
which can be exploited by a malicious server when the victim client
connects to it.

The main format string can be exploited through a malformed CLASS
parameter of the DLMGR command but another one seems to be exploitable
through the forcing of the download of a malformed package (PKG).
Some older games instead can be exploited through a malformed LEVEL
parameter of the WELCOME command.

The bug is caused by the calling of _vsnwprintf_s or _vsnwprintf for
building an error message to visualize to the user (for example for a
missing class) using a max size of 4 kilobytes and, naturally, without
passing the needed format argument.


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===========
3) The Code
===========


http://aluigi.org/testz/unrealts.zip
http://aluigi.org/poc/unrealcfs.txt

- unrealts 7777 unrealcfs.txt
  (or "unrealts -x 2 7777 unrealcfs.txt" for the Unreal 3 engine, use
  -x for others)
- open the console of your client (~) and type: open 127.0.0.1:7777


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======
4) Fix
======


No fix


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