From: Jose Maria Lopez (jkerouac@bgsec.com)
Date: Thu Sep 02 2004 - 12:55:53 EDT
El jue, 02 de 09 de 2004 a las 05:36, vinay mangal escribió:
> Dear all,
>
> Thanks for your suggestions. May be I am not able to define my question
> properly.
>
> This problem is strictly with in company internet access firewall and in the
> LAN only. In a company, policy for Internet access says it is through IP
> only. The others can not browse the internet. This policy is implemented on
> firewall. Few smart guys have installed free proxy server running on non
> default ports and distributed the internet access to their friends. The
> firewall sees the traffic coming from the authorized IP and does not stop
> them. We want to know who has installed proxy on there machine.
>
> I hope, I am able to clearly define my question. Thanks
>
>
> vinay
What's happening in your LAN is called firewall tunneling of firewall
piercing, and it's one of the security threats one have to deal of when
you have a firewall. If the proxies are running in non-standard ports
then you should close those ports in the firewall, if you have the
default policy to block only some ports you should turn to block all
ports and open only the ports you use (80, 21, 22, etc), or at least
only admit the packets coming from an established connection, so you
never let other machines to initiate connections to non-standard ports
from outside your LAN.
You could also use a sniffer like ethereal to watch the traffic at your
firewall and see what IP addresses are tunneling traffic through
standard or non standard ports, you probably can discern normal traffic
from tunneled traffic with ethereal.
--
Jose Maria Lopez Hernandez
Director Tecnico de bgSEC
jkerouac@bgsec.com
bgSEC Seguridad y Consultoria de Sistemas Informaticos
http://www.bgsec.com
ESPAÑA
The only people for me are the mad ones -- the ones who are mad to live,
mad to talk, mad to be saved, desirous of everything at the same time,
the ones who never yawn or say a commonplace thing, but burn, burn, burn
like fabulous yellow Roman candles.
-- Jack Kerouac, "On the Road"
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