From: Chris Brenton (cbrenton@chrisbrenton.org)
Date: Thu Sep 02 2004 - 14:06:22 EDT
On Wed, 2004-09-01 at 23:36, vinay mangal wrote:
>
> 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.
This will be easy or hard, depending on just how smart the "smart guys"
are. ;-)
Someone else posted saying to use ngrep. Its still your friend in this
case. Most proxies stamp an "X-Forwarded-For" field into the payload so
you can use ngrep to key in on that. Something like:
ngrep -q 'X-Forwarded-For' port 80
in the path of the firewall will do the trick. Now for the bad news,
most proxies also let you remove that "X-Forwarded-For" field, so if
they are *really* smart and have done this you will not catch it.
BTW, if you catch one box, do a full TCP port scan of that IP to find
the proxy server, and then start checking all your internal IP's for
that same open port. When I've seen this before one bad apple starts the
whole thing and then others just copy their config.
HTH!
Chris
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