NULL pointer in Ventrilo 3.0.2

2008-08-1500:00:00

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                         Luigi Auriemma

Application: Ventrilo
http://www.ventrilo.com
Versions: <= 3.0.2
Platforms: Windows, Linux i386, Solaris SPARC, Solaris x86, FreeBSD
i386, NetBSD i386, Mac OSX PowerPC
Bug: NULL pointer
Exploitation: remote, versus server
Date: 13 Aug 2008
Authors: Andre Malm Luigi Auriemma
web: sheepa.org e-mail: [email protected]
web: aluigi.org

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

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1) Introduction

Ventrilo is one of the most knwon and used voice chat softwares for
gamers.

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2) Bug

Despite the vice of the Ventrilo developers of changing the protocol of
their application enough often (like the recent senseless additional
encryption keys located on their centralized servers needed for the
handshake and the in-game packets of the 3.x servers), the first packet
sent to a Ventrilo server has ever the same format on any new and old
version: type 0, version and two random strings.

If the server receives a version string different than its one it sends
an "Incompatible version" error message to the client and skips the
instructions that create the random keys used for the encryption and
decryption of all the subsequent packets.

So if an attacker supplies an invalid version and sends another packet
with any content in it, the server crashes due to the key assigned for
the decryption of the client's packets which is still unitialized (in
fact the NULL pointer exception happens just in the decryption
function).

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