Re: Advice on multiple packet capture

[Matt Olney <molney () sourcefire com>]

Hint
  -  Pay attention to client side reassembly, the default is not to
reassemble on traffic TO the client.

Matt

On Wed, Jan 14, 2009 at 5:38 AM, Leon Ward <seclists () rm-rf co uk> wrote:
> Hi
> The flowbit is only valid for the stream where it has been set.
> The two GET's for the JPG files (as you stated) will be in separate requests
> so flowbits wont help you here.
> Instead of focusing on the URI of the GET, how about you focus on the HTML
> source of the web page that contains the <img src="a.jpg"> tags?
> Hints
>  - Check out http_inspect's flow_depth
>  - Pay attention to the encoding used by the webserver serving the HTML.
> -Leon
>
> On 14 Jan 2009, at 07:39, pieter claassen wrote:
>
> Yes, I agree. What you need to do is write two sets of rules that are
> statefull:
>
> Something like this:
> Rule1: uricontent:a.jpg; flowbits:set, ajpg.seen; noalert
> Rule2: flowbits:isset,ajpg.seen, uricontent:b.jpg; msg: "saw a.jpg and then
> b.jpg"
> Rule3: uricontent:b.jpg; flowbits:set, bjpg.seen; noalert
> Rule4: flowbits:isset,bjpg.seen; uricontent:a.jpg; msg: "saw b.jpg and then
> a.jpg"
>
> Regards,
> Pieter
>
> On Mon, Jan 12, 2009 at 10:23 PM, jeffs <jeffs () speakeasy net> wrote:
> > I've been using Snort and still consider myself a newbie although I am
> > fairly familiar with writing basic rules.  Unfortunately, the feat I
> > need to perform may need a more advanced set of eyes so I am hoping
> > someone on this list may be able to help me out.
> >
> > I need to get only 1 alert on two separate GET requests that contain
> > different .jpg file names.
> >
> > For example, there is a web page, it contains A.jpg and B.jpg.  If
> > someone looks at it I want to be able to get one alert but NOT if they
> > look at a different page which contains A.jpg and NOT B.jpg or still yet
> > a different page that contains B.jpg and NOT A.jpg.  Only on the page
> > the contains BOTH .jpgs should generate 1 alert.
> >
> > I've tried the within keyword but I believe this only searches within a
> > single packet and as the two separate jpg files are sent via two
> > separate GET requests, I believe I am working with more than one packet,
> > am I correct in that assumption?
> >
> > thanks for any advice.
> >
> >
> >
> >
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