Re: [help,urgent] Using PCRE to match packets in hex

[JJ Cummings <cummingsj () gmail com>]

Even if using regex you need a content anchor... It is considered best practice and helps dramatically in terms of 
performance and overall rule overhead!

Sent from the iRoad

> On Oct 27, 2013, at 13:33, Yoyo Lam <mtcyoyo () gmail com> wrote:
>
> These would be samples for checking. They are fetched using Wireshark. You can find it at the first packets to 
> 130.37.198.87.
> A sample of packet that I want to match is already in the regex site I put before.
> I thought there would be no problem to my packet. I just want to know how to use my pattern to match against the hex 
> dump of the packet.
>
> I didn't use content since I don't really get how to use it properly, and with my programming experience, I am more 
> familiar with regex. And it seems that using pcre alone is ok. (not thoroughly tested)
>
> Yoyo
>
>
> 2013/10/27 Jeremy Hoel <jthoel () gmail com>
> > Without a pcap of the data you're trying to hit on its hard to tell.. but this section mentions you might want a 
> > content part of the rule also.
> >
> > http://manual.snort.org/node32.html#SECTION004523200000000000000
> >
> > > On Oct 27, 2013 12:43 PM, "Yoyo Lam" <mtcyoyo () gmail com> wrote:
> > > Hello experts,
> > >
> > > I have a problem about PCRE. I wrote a PCRE pattern that perfectly matches a certain message, and I checked in some 
> > > regex checker and there is no problem. But when I put it in a Snort rule with the B modifier, it doesn't work. 
> > > Please help me to figure what happened.
> > >
> > > The PCRE Check page:
> > > http://www.phpliveregex.com/p/1In
> > >
> > > My Snort rule:
> > > alert tcp any any -> any any (pcre:"/([0-9a-fA-F]{2})13([0-9a-fA-F]{2}){8}(77696e646f7773|6c696e7578)/B"; msg:"Some 
> > > message"; sid:1234567; rev:1;)
> > >
> > > Please help me by either
> > > 1) Telling me what I have forgotten to add/change/remove;
> > > 2) Give me the working rule :D
> > > 3) Any way that can solve this fast
> > >
> > > This is quite urgent, so please help me asap.
> > >
> > > Best regards,
> > > Yoyo
> > >
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> <drop.pcapng>
> <drop2.pcapng>
> ------------------------------------------------------------------------------
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------------------------------------------------------------------------------
October Webinars: Code for Performance
Free Intel webinars can help you accelerate application performance.
Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from 
the latest Intel processors and coprocessors. See abstracts and register >
http://pubads.g.doubleclick.net/gampad/clk?id=60135991&iu=/4140/ostg.clktrk

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