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Re: Sourcefire VRT Certified Snort Rules Update 2010-03-17

From: Mike Cox <mike.cox52 () gmail com>
Date: Tue, 23 Mar 2010 20:12:33 -0500
god if it is true that snort doesn't decode gzip (before v2.5/6) then I
might be sick ... I'm missing detecting tons of stuff.  Does suricata
support matching on un-gzipped data? I could have sworn I saw daemonlogger
gzip pcaps and then looked and saw gzip decoded snort logs on alerts.  Am I
wrong?  Say it isn't so!

-Mike Cox

On Tue, Mar 23, 2010 at 6:49 PM, Joel Esler <joel.esler () me com> wrote:


This is a difficult thing to do, as it requires some good processing power
to be able to do this.

--
Joel Esler
Sent from my iPhone

On Mar 23, 2010, at 6:41 PM, Mike Cox <mike.cox52 () gmail com> wrote:

Wait ... the http_inspect preprocessor didn't decode gzip and match against
the unzipped data until 2.8.6 (and/or 2.8.5)?  If so, this should have been
put in 5+ years ago.  I could be making a false assumption here which I
probably am because I can't imagine that snort didn't do this before now....

-Mike Cox

On Tue, Mar 23, 2010 at 5:27 PM, Joel Esler < <joel.esler () me com>
joel.esler () me com> wrote:


Will,

I'm not saying that 2.8.6 will solve these problems, but it definitely
will help.  For example the following is new functionality (and/or keywords)
either in recent versions of 2.8.5 or within Snort 2.8.6.

(This information comes out of the Snort Manual)

http_client_body -- The http client body keyword is a content modifier
that restricts the search to the body of an HTTP client request.
http_cookie -- The http cookie keyword is a content modifier that
restricts the search to the extracted Cookie Header field of a HTTP client
request or a HTTP server response
http_raw_cookie -- The http raw cookie keyword is a content modifier that
restricts the search to the extracted UNNORMALIZED Cookie Header field of a
HTTP client request or a HTTP server response
http_header -- The http header keyword is a content modifier that
restricts the search to the extracted Header fields of a HTTP client request
or a HTTP server response
http_raw_header -- The http raw header keyword is a content modifier that
restricts the search to the extracted UNNORMALIZED Header fields of a HTTP
client request or a HTTP server response
http_method -- The http method keyword is a content modifier that
restricts the search to the extracted Method from a HTTP client request.
http_uri -- The http uri keyword is a content modifier that restricts the
search to the NORMALIZED request URI field . Using a content rule option
followed by a http uri modifier is the same as using a uricontent by itself
http_raw_uri -- The http raw uri keyword is a content modifier that
restricts the search to the UNNORMALIZED request URI field
http_stat_code -- The http stat code keyword is a content modifier that
restricts the search to the extracted Status code field from a HTTP server
response.
http_stat_msg -- The http stat msg keyword is a content modifier that
restricts the search to the extracted Status Message field from a HTTP
server response.
http_encode -- The http encode keyword will enable alerting based on
encoding type present in a HTTP client request or a HTTP server response

We also have the ability to uncompress the compressed data in gzip in
http_inspect now:
inspect_gzip: This option specifies the HTTP inspect module to uncompress
the compressed data (gzip/deflate) in HTTP response.

Just some of the new options.

Joel

On Mar 23, 2010, at 6:16 PM, Will Metcalf wrote:


Joel,

What of these potential evasions are addressed specifically by 2.8.6?
Unless snort has made fundamental changes to the way it operates I
think these issues will be very difficult to overcome but as I said,
these are not snort specific issues. There is a reason why most NIDS's
commercial or otherwise are blind to this stuff, it's because
client-side is a really freaking hard problem to solve.  This is
especially true at multi-gigabit speeds, even if you are sporting
latest 32 core xeon 55xx server or something.

Regards,

Will
On Tue, Mar 23, 2010 at 4:51 PM, Joel Esler < <joel.esler () me com>

joel.esler () me com> wrote:

I would encourage a look at the new http_inspect in 2.8.6.

--
Joel Esler
Sent from my iPhone

On Mar 23, 2010, at 5:11 PM, Will Metcalf <<william.metcalf () gmail com>

william.metcalf () gmail com> wrote:



1) sid:15013 will only set the flowbit if I download the PDF from a
webserver (alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS).
What if the malicious pdf is sent via email -- or another method?
16490 will never even run because the flowbit is not set.   Right?

2) From sid:16490, I gather that it will only trigger if the

malicious

PDF communicates with an external webserver on an HTTP_PORT and the
exploit is then sent from that server (alert tcp $EXTERNAL_NET
$HTTP_PORTS -> $HOME_NET any -- flow to server).  Is that correct?
What if the malicious PDF is configured to communicate on a non
HTTP_PORT with the malicious webserver.


Or if encryption is used, or if the client side exploit isn't
contained within the first x bytes of the payload you have configured
for flow_depth, or if the client side exploit can be encoded in
javascript, etc. etc. etc.  This isn't a snort specific problem all
network based IDS's suck at detecting client-side exploits.  They just
aren't the right tool for the job, despite what your vendor my share
with you via their marketing slides ;-).


This brings me to a question.   What are most of you doing for
443/tcp.  Do you include it in your HTTP_PORTS variable or not?   By
default I believe it is NOT included.   Wouldn't this mean that
another really easy way to avoid detection of this particular
vulnerability being exploited would be to have your malicious pdf
connect to port 443 instead of 80 outbound?  (In metasploit, setting
LPORT to anything aside from 80?)


But you are filtering egress traffic right?  And using a proxy to
enforce protocol behavior right?  Also you have sort of ASLR/buffer
overflow type protection on your clients right? Via some Host IPS
product or something like EMET?




<http://www.microsoft.com/downloads/details.aspx?FamilyID=4a2346ac-b772-4d40-a750-9046542f343d&displaylang=en>
http://www.microsoft.com/downloads/details.aspx?FamilyID=4a2346ac-b772-4d40-a750-9046542f343d&displaylang=en


Regards,

Will




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--
Joel Esler
 <http://blog.joelesler.net>http://blog.joelesler.net




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