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Rogue activity methodology (was: Tool to find hidden web proxy server)
From: Chris Brenton <cbrenton () chrisbrenton org>
Date: Sun, 05 Sep 2004 05:52:40 -0400

On Wed, 2004-09-01 at 13:44, Bénoni MARTIN wrote:

Well...
 -  The easier way is to scan your whole network and see the machines which are up (nmap -sS xxx.xxx.xxx.0/24). 
Maybe, you will find a strange machine which can be your proxy.

I have to say, I'm a bit surprised at how many people chimed in with
"scan your whole network". This seems like a lot of work (and traffic)
given the situation Vinay described. Just to go back over the "facts" he
has given us:

* Only certain IP's are permitted outbound HTTP access
* Suspects one or more of these IPs have setup a rogue proxy
* Unauthorized users may be accessing the Internet via the proxies
* Suspects the proxies are on a non-standard ports (implies he might
have already checked the standard ports)
* No indication if the internal network is switched or repeated
* No indication of the OS being used
* No indication of whether he has admin access to these systems
* No indication of how big the internal network may be
* No indication of how many systems are permitted outbound HTTP access

So if he's running a class B, nmap is going to spend a whole lot of time
saturating the wire. That and there is no guarantee that the systems in
question will be "up" when nmap tries to hit their IP. Finally, nmap is
probably going to produce a ton of data that needs to be sorted through.
This will include a lot of false positives in the form of listening
ports that are not the proxy servers in question. Bottom line, lots of
work and no guarantee of resolving the problem. 

Don't get me wrong, nmap is an awesome tool, but I guess I was trying to
hit this from a methodology stand point. In other words, what's the
easiest way to isolate the proxy traffic signature from "normal" traffic
patterns? If you can do that, your false positives are minimal and thus
the amount of "work" you have to do to resolve the problem is minimal.

This is why myself and a few others chimed in with methods that would
isolate proxy communications from normal traffic flow (look for
"CONNECT" between local systems or "X-Forwarded-For" headed to the
Internet, etc.). If you get a "hit", it is extremely unlikely to be a
false positive. So by isolating what is unique about proxy
communications you reduce the error rate as well as the amount of work
that needs to be done to solve the problem.

Just wanted to throw the above out there for comment/discussion,
Chris



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