Thanks for the info and explanation Will.
I did a little more testing and thought I would mention what I found in
case it makes any difference.
Turns out the traffic between the internal http proxy and users is
alerted on if I remove ONLY the "established" part of the rule flow
option.
Also, the proxy is a linux based McAfee SCM appliance that uses the
built-in mozilla/firefox/IE client side proxy settings.
I also noticed that if I do define a default http_inspect_server config
line, then even with the "established" part of the rule flow option
used, the IDS does NOT alert on the traffic.
Aka, if I do NOT define a default http_inspect_server config line, AND I
remove the "established" part of the rule flow option, then the traffic
between the internal http proxy and users is alerted on, as I would
like. Now, I can't really go through all rules and remove the
established portion of the flow section. I did define some
http_inspect_server config lines for our internal webservers.
Does any of the above offer any ideas as to what I could tweak other
than every single rule that I want to be alerted on?
Would creating a custom http_inspect_server config line for the internal
http proxy server perhaps allow this traffic to be alerted on? Any
ideas on what options to use if this is the route to go?
-----Original Message-----
From: Will Metcalf [mailto:william.metcalf@gmail.com]
Sent: Monday, November 26, 2007 12:10 PM
To: Gould, Scott
Cc: Snort-users@lists.sourceforge.net
Subject: Re: [Snort-users] Alert on contents of proxy traffic
Well first off you are not going to see very much of the payload
returned from an external webserver because of the default flow_depth in
http_inspect. You can set flow_depth to 0 to see the entire payload at
the expense of deep sixing your IDS. In addition if you are wrapping
requests inside of a Winsock proxy client (ISA Server) snort may not
fire because it does not know how to decode this protocol.
Regards,
Will
On Nov 26, 2007 10:47 AM, Gould, Scott <scott.gould@gogstats.org> wrote:
Thanks for the prompt reply
Snort version 2.4.5
Proxy runs on port 80
An example rule would be just about any web content. For example, a
rule that triggers on the outside between the internal proxy server
and external webservers with the following options:
alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any (msg:"Test
Phrase"; content:"test Phrase"; nocase;
flow:to_client,established;...........
Would only trigger on the inside between the internal client and
internal http proxy server, if I remove the flow info:
alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any (msg:"Test
Phrase"; content:"test Phrase"; nocase;
......................................
For testing purposes I have set the $EXTERNAL_NET and $HOME_NET to
any.
BTW, there are 2 different snort instances here. But, other than
server specific settings for some of the preprocessors (servers which
are not involved in this scenario), the configs are the same for
testing purposes.
Scott
-----Original Message-----
From: rmkml [mailto:rmkml@free.fr]
Sent: Monday, November 26, 2007 9:00 AM
To: Gould, Scott
Cc: rmkml@free.fr
Subject: Re: [Snort-users] Alert on contents of proxy traffic
Hi Scott,
what snort version you use please ?
maybe send example (traffic/alert) ?
and send snort.conf ?
what port on your proxy please ? (81 ? 3128 ? 8000 ? 8080 ?)
Interesting think with snort 280 and port var features !
Best Regards
Rmkml
On Mon, 26 Nov 2007, Gould, Scott wrote:
Date: Mon, 26 Nov 2007 11:29:31 -0500
From: "Gould, Scott" <scott.gould@gogstats.org>
To: Snort-users@lists.sourceforge.net
Subject: [Snort-users] Alert on contents of proxy traffic
Here is the setup:
Snort listening on traffic flowing between internal users and http
proxy. Snort listening on traffic flowing between internal proxy
and external web servers. As anticipated, many rules are triggered
on the
traffic between the internal proxy and the external web servers.
BUT,
same rules are not triggered on same traffic between the http proxy
and the internal users.
What I am trying to achieve is see an alert between the internal
http proxy and external webservers, and correlate to an alert on the
same traffic, but as it flows between the internal users and the
internal http proxy. For some reason, only the outside traffic is
triggering the alert. To confirm snort and variables are setup
correctly for testing so that I should see alerts, I confirmed can
trigger rules on ICMP traffic between the internal http proxy and
the internal users.
It appears that the proxy is doing something to the traffic as it
flows between the internal http proxy and the users, so that is not
detected by snort rules.
Any thoughts or suggestions on where to start tinkering?
Thanks in advance,
Scott
Scott Gould
Senior Network & Systems Analyst
Gynecologic Oncology Group
Statistical & Data Center
scott.gould@gogstats.org
716-845-5702
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