From: R. DuFresne (dufresne@sysinfo.com)
Date: Thu Sep 02 2004 - 13:56:10 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
> > 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.
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.
Thanks,
Ron DuFresne
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