Re: Understanding within

[Joel Esler <jesler () sourcefire com>]

On Aug 15, 2012, at 2:01 PM, James Lay <jlay () slave-tothe-box net> wrote:
> On 2012-08-15 11:41, lists () packetmail net wrote:
> > On 08/15/12 12:33, Joel Esler wrote:
> > > You cannot apply content keywords to pcre.
> > >
> > > (So, no, you can't do what you are asking)
> >
> > Right but he could use the /R flag (like distance:0) to make the PCRE
> > relative
> > to the last content match.  You could also just PCRE-up your within.
> >
> > Example:
> >
> > content:"bleh"; content:"blah" within:14;
> >
> > pcre:"/bleh[^\r\n]{0,10}blah/";
> >
> > PCRE version 7.8 2008-09-05
> >
> >  re> /bleh[^\r\n]{0,10}blah/
> > data> blehblah
> > 0: blehblah
> > data> bleh1234567890blah
> > 0: bleh1234567890blah
> > data> bleh12345678901blah
> > No match
> > data>
>
> Thanks gents...this does help.  Not to beat a dead horse here...here's 
> the original snippet from the email:
>
> The reference number for this fax is <a 
> href="hxxp://pixeljunks.de/YRmJLNJv/index.html">min1_did12-1345023267-7176853217-25
>
> For things like this should I just forget about the within statement, 
> knowing that:
>
> content:"<a href=|22|http:"; fast_pattern; pcre:"/\x2f[a-z]{8}\x2f/i";


James:

SID: 22088 covers these redirection attempts.  

But maybe 
alert tcp $EXTERNAL_NET any -> $HOME_NET 25 (msg:"something bad this way comes"; flow:to_server,established; file_data; 
content:"<a href="|22|http|3a"; content:"index.html"; distance:0; within:30; pcre:"/\x2f[A-Z\d]{8}\x2f/i";   
metadata:service smtp;)

?

--
Joel Esler
Senior Research Engineer, VRT
OpenSource Community Manager
Sourcefire


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