[Snort-sigs] PCRE and normalized content

Paul Schmehl pschmehl_lists at ...3425...
Wed Jan 13 21:23:04 EST 2010


Apparently I need to read your snort manual.  The one I was looking at 
didn't have all those options.  :-(

Sure, I won't match 1>2, but I'll still match all equalities, which is 
important to me.  I'm already catching a bunch of stuff we were missing 
previously.

--On January 13, 2010 6:08:52 PM -0600 "Rodrigo Montoro(Sp0oKeR)" 
<spooker at ...2420...> wrote:

>
> Paul,
>
> I think you should read snort manual  =)
>
> Table 3.8: Snort specific modifiers for pcre
> R Match relative to the end of the last pattern match. (Similar to
> distance:0;)
> U Match the decoded URI buffers (Similar to uricontent and http uri)
> P Match normalized HTTP request body (Similar to http client body)
> H Match normalized HTTP request header (Similar to http header)
> M Match normalized HTTP request method (Similar to http method)
> C Match normalized HTTP request cookie (Similar to http cookie)
> B Do not use the decoded buffers (Similar to rawbytes)
> O Override the configured pcre match limit for this expression (See
> section 2.1.3)
>
> Anyway this rules will fail with a simples and 1<2 .
>
> I tried once to write a rules but there are to many ways to write the
> same query  take a look at this thread
> http://lists.emergingthreats.net/pipermail/emerging-sigs/2008-June/00069
> 8.html
>
> Anyway I don't thing this list is about writing new rules =)
>
> Regards,
>
> On Wed, Jan 13, 2010 at 9:52 PM, Paul Schmehl <pschmehl_lists at ...3425...>
> wrote:
>> This string: %20%61%6E%64%20%31%3D%31
>> equals this string: ' and 1=1'
>> after normalization.  You can pick this up in a rule by using
>> uricontent instead of content.  But what do you do about PCRE?  Is
>> there a way to get PCRE to match against normalized content?  Or will
>> it only match against non-normalized content?
>>
>> I'm working on sql injection rules and using the following pcre:
>> pcre:"/and\s(\d+)=\1/";
>>
>> It works fine on 1=1 or 54=54, but fails on %31%3D%31, apparently
>> because it's attempting to match against the non-normalized content.
>>
>> --
>> Paul Schmehl, Senior Infosec Analyst
>> As if it wasn't already obvious, my opinions
>> are my own and not those of my employer.
>> *******************************************
>> "It is as useless to argue with those who have
>> renounced the use of reason as to administer
>> medication to the dead." Thomas Jefferson
>>
>>
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>
>
>
> --
> Rodrigo Montoro (Sp0oKeR)
> http://www.spooker.com.br
> http://www.twitter.com/spookerlabs
> http://www.linkedin.com/in/spooker



Paul Schmehl, If it isn't already
obvious, my opinions are my own
and not those of my employer.
******************************************
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