Snort mailing list archives

Re: Help with a rule


From: Luis Daniel Lucio Quiroz <luis.daniel.lucio () gmail com>
Date: Fri, 6 Mar 2009 12:22:42 -0600

Thx

However I apply the rule:

alert tcp $HOME_NET $HTTP_PORTS -> $EXTERNAL_NET any (msg:"text mime type 
detected in web traffic"; flow:established,from_server; content:"Content-Type 
|3A| text/"; nocase; sid:1000001; rev:1; \
 classtype:web-application-activity;)

I got

ERROR: Warning: rules/local.rules(10) => Unknown keyword ' sid' in rule!
Fatal Error, Quitting..


What I missing?  regards,

LD


On Friday 06 March 2009 08:12:54 Alex Kirk wrote:
First of all, depending on just how much you want to log, going with
"alert" instead of "log" and skipping the "tag:session;" may be smart - it
would be easy to overload your IDS with this if it's not very powerful, or
if it's attempting to do anything else.

That said, the rule you'd want for a purpose like this - which I'm sure you
realize is only stopgap, since it's really the web app's job to be doing
logging like this - would look more like:

alert tcp $HOME_NET $HTTP_PORTS -> $EXTERNAL_NET any (msg"text mime type
detected in web traffic"; flow:established,from_server;
content:"Content-Type|3A| text/"; nocase;
classtype:web-application-activity; sid:1000001; rev:1;)

Key differences:

* $HTTP_PORTS is actually a default Snort variable, as opposed to
$PORT_HTTP * Since the Content-Type header will be present in things coming
*from* the web server, and not going to it, the direction is set properly
now * "flow:established,from_server"; will save Snort a lot of work looking
at packets that will never match, based on them being in the wrong part of
the TCP stream
* The "|3A|" in the content is necessary, because a colon in a content
clause will cause a syntax error
* Removed "http_header", since it's for client requests, and you're looking
for server responses
* Removed quotes from the classtype, as that's another fatal syntax error

Hope that helps.

Alex Kirk
Research Analyst
Sourcefire, Inc.

On Thu, Mar 5, 2009 at 11:21 PM, Frank Knobbe <frank () knobbe us> wrote:
On Thu, 2009-03-05 at 21:38 -0600, Paul Schmehl wrote:
Logs al http packets that has a text/* mime type.

alert tcp $EXTERNAL_NET any -> $HOME_NET $PORT_HTTP (msg:"text mime
type detected in web traffic"; content:"Content-Type: text/";
http_header; classtype:"web-application-activity"; sid:1000001; rev:1;)

Does it capture all packets? Does it log? (Your rule alerts)

Strictly speaking, you probably would want to use the following
modifications for his specific need:

log tcp any any -> any $PORT_HTTP (msg:"text mime type
detected in web traffic"; content:"Content-Type: text/"; http_header;
classtype:"web-application-activity"; sid:1000001; rev:1; tag:session;)

:)

Cheers,
Frank



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-OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise
-Strategies to boost innovation and cut costs with open source participation
-Receive a $600 discount off the registration fee with the source code: SFAD
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