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Re: Tool to find hidden web proxy server
From: "R. DuFresne" <dufresne () sysinfo com>
Date: Thu, 2 Sep 2004 13:56:10 -0400 (EDT)

On 2 Sep 2004, Jose Maria Lopez wrote:

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

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


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.

Actually if only doing with with allowing new and or established though,
providing ths FW in question is stateful, will not accomplish the task,
the way to do this is to only allow in and out from specific IP's that
should be serving the content being provided.

Either internally scanning the network fr offending services and/or
snooping traffic will be enugh to determine who is trying to break policy.
There is no trick in this and any of the tools mentioned in the tread
should do the trick.


Ron DuFresne
        admin & senior security consultant:  sysinfo.com

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