Re: SOLVED - Trouble with HTTP status message rule

[Research <research () nativemethods com>]

On Mar 12, 2015, at 7:04 PM, Joel Esler (jesler) <jesler () cisco com> wrote:

> Keep in mind from_server = to_client.
>
>
> > On Mar 12, 2015, at 6:02 PM, Research <research () nativemethods com> wrote:
> >
> >
> > On Mar 12, 2015, at 5:57 PM, Research <research () nativemethods com> wrote:
> >
> > > Hello,
> > >
> > > I am currently writing a rather basic rule to track 404 resource not found instances in Snort on a web server.  
> > > While I am aware that the logs for the web server process themselves track this, I’d like to generate a Snort rule 
> > > that does the same for some testing.
> > >
> > > Currently my rule is:
> > >
> > > alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS \
> > >         
> > > (msg: "Web resource not found"; flow:established,to_server; content:"404"; http_stat_code; priority:4; sid:2000110; 
> > > rev:001;)
> > >
> > > I have used the http_stat_code modifier for the content, but when I attempt to locate a non-existent resource:
> > >
> > > http://mywebserver.com/notthere
> > >
> > > …the rule does not fire.
> > >
> > > I was wondering what I am missing.
> > >
> > > Thanks
> >
> > Discovered what I was doing wrong.  Should have been tracking this as a response *FROM* the server, not inbound 
> > traffic.
> >
> > The following rule solves the problem:
> >
> > alert tcp $HOME_NET $HTTP_PORTS -> $EXTERNAL_NET any \
> >         
> > (msg: "Web resource not found"; flow:established,from_server; content:"404"; http_stat_code; priority:4; 
> > sid:2000110; rev:001;)


Good point!

With the rule I also swapped the direction after the protocol:

        alert tcp $HOME_NET $HTTP_PORTS -> $EXTERNAL_NET any \ (snip)

…instead of incoming traffic:

                alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS \ (snip)

…and now the rule fires.

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