[Snort-sigs] Suggested pcre addition to 1:6251

Jason Wallace jason.r.wallace at ...2420...
Wed Nov 24 14:43:48 EST 2010


Or maybe a user_agent: rule option that limits the search to the
user-agent header?



On Wed, Nov 24, 2010 at 2:31 PM, CunningPike <cunningpike at ...2420...> wrote:
> Hi there,
>
> I get a lot of false positives on the following rule:
>
> alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"SPYWARE-PUT
> Adware hotbar runtime detection - hostie user-agent";
> flow:to_server,established; content:"User-Agent|3A| "; nocase;
> content:"hostie"; distance:0; nocase; threshold:type limit, track
> by_src, count 1, seconds 300; metadata:policy security-ips alert;
> reference:url,www.spywareguide.com/product_show.php?id=481;
> reference:url,www3.ca.com/securityadvisor/pest/pest.aspx?id=453075474;
> classtype:misc-activity; sid:6251; rev:5;)
>
> from content like this:
>
> GET /2.5.1/js/CF_insight.min.js HTTP/1.1..Accept: */*..Referer:
> http://www.theweathernetwork.com/weather/cabc0308..Accept-Language:
> en-us..Accept-Encoding: gzip, deflate..User-Agent: Mozilla/4.0
> (compatible; MSIE 6.0; Windows NT 5.1; SV1)..Connection:
> Keep-Alive..Host: scripthostie6.crowdfactory.com....
>
> I'm wondering would the addition of the following pcre help keep the
> match within the User-Agent field:
>
> pcre:"/User-Agent:[^\x0D\x0A]*hostie.*/smi";
>
> or would it allow for evasion of some kind.
>
> If this is a could idea, there are probably other UA-based sigs that
> could benefit from the same treatment.
>
> Thoughts?
>
> CP
>
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