Re: Tool to find hidden web proxy server

["Gary E. Miller" <gem () rellim com>]

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Yo Jose!

On Thu, 2 Sep 2004, Jose Maria Lopez wrote:

> But if you allow in and out from specific ports you have at least a
> second level of security over what the original poster said it had.
> Only allowing out from some IPs it's possible, but I find it very
> difficult to make rules for the outer IPs, having in mind the original
> poster wants to have internet connection from the LAN for that
> machines.

If you leave just ONE port open, then an insider can use it to tunnel
out.  That one port is often DNS/udp.  You have to work very, very,
hard to filter out IP over DNS/udp.  You could force the use of
an internal DNS server, but if it allows any recursive lookups out
of the firewall then game over.

This /. describes how to do it:
        http://slashdot.org/articles/00/09/10/2230242.shtml

The insider does not even need an open port.  Only TCP/IP (proto 6) and
TCP/UDP (proto 17) use "ports".  The insider can just use a "portless"
protocol like TCP/ICMP (proto 1), TCP/ESP (proto 50), TCP/AH (proto 51),
etc.

There are several IPSEC stacks available as freeware that use TCP/ESP
and TCP/AH.

RGDS
GARY
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Gary E. Miller Rellim 20340 Empire Blvd, Suite E-3, Bend, OR 97701
        gem () rellim com  Tel:+1(541)382-8588 Fax: +1(541)382-8676

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