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                             Luigi Auriemma

Application:  Half-Life engine
              http://half-life.sierra.com
              http://www.steampowered.com
Versions:     before the 07 July 2004 (both Steam and not-Steam)
Platforms:    Windows and Linux
Bug:          writing on a read-only memory zone causing crash
Risk:         high
Exploitation: remote, versus server and client
Date:         12 July 2004
Bug found by: Terry Henning (aka Soul Beaver)
Advisory:     Luigi Auriemma
              e-mail: aluigi@altervista.org
              web:    http://aluigi.altervista.org


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


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


Half-Life is the most famous FPS game existent, no doubts.
It has been developed by Valve (http://www.valvesoftware.com) and has
been released in the far 1998, but also after all this time it
continues to be the most played game with its MODs like Counter-Strike,
Natural selection, Sven-coop and many others.
Everyday there are about 37.000 servers online!

As already specified in the header of this advisory I want to underline
that this bug has been found by Terry Henning.


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2) Bug
======


The problem is a crash of the game (both servers and clients are
vulnerables) caused by a malformed packet.
Each Half-Life packet is composed by the first 8 bytes used to track
packets and to reassemble splitted data, just this second feature is
the cause of the crash because the game doesn't correctly manage the
empty splitted packets (so composed by the first 8 bytes only).
The crash is the effect of the copying of data to a read-only part of
memory (.reloc of swds.dll).

An example of malicious packet is the following:

  "\xFE\xFF\xFF\xFF\x00\x00\x00\x00"

Naturally spoofing is possible.


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3) The Code
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http://aluigi.altervista.org/poc/hlboom.zip


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4) Fix
======


If you use Steam you are already patched by some days.

To note that Half-Life is now supported ONLY via Steam, the half hated
or loved content management system of Valve.
The latest non-Steam patch is stopped at the 1.1.1.0 (affected by other
worst bugs) and is no longer supported.


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--- 
Luigi Auriemma
http://aluigi.altervista.org