[Snort-devel] BUG: corner case involving http_cookie

Will Metcalf william.metcalf at ...2499...
Mon Mar 15 11:08:14 EDT 2010


Thanks Steve!

Regards,

Will

On Mon, Mar 15, 2010 at 10:06 AM, Steven Sturges
<steve.sturges at ...402...> wrote:
> Will et al--
>
> We're looking into these issues... Will follow up in the next
> day or so.
>
> Cheers
> -steve
>
> Will Metcalf wrote:
>> Seems using http_(cookie|header) with isdataat acts the same way
>> src/snort -k none -q -A console -c etc/snort.conf -l ./ -r
>> /home/coz/oisfsearchnums.pcap
>>
>> #these rules fail to fire even though the isdataat check isn't
>> relative client/server flow depth both set to 0
>> #alert tcp any any -> any any (msg:"e6504ae48c99f09df7f58996aacbb6b0 +
>> http_cookie + isdataat"; content:"e6504ae48c99f09df7f58996aacbb6b0";
>> http_cookie; isdataat:596; classtype:bad-unknown; sid:104; rev:1;)
>> #alert tcp any any -> any any (msg:"our website host header +
>> http_header + isdataat"; content:"Host|3A|
>> www.openinfosecfoundation.org"; http_header; isdataat:596;
>> classtype:bad-unknown; sid:105; rev:1;)
>>
>>
>> On Thu, Mar 11, 2010 at 10:02 AM, Will Metcalf
>> <william.metcalf at ...2499...> wrote:
>>> Fails on byte_jump as well, additionally http_header appears to act
>>> the same way.
>>>
>>> Regards,
>>>
>>> Will
>>>
>>> #test 73 http_cookie + byte_jump.
>>> #hmm interesting using http_cookie in combination with byte_jump seems
>>> to fail always. Removing either the byte_jump check or the http_cookie
>>> modifier will cause this sig to fire.  Notice that the byte_jump
>>> #check isn't even relative to the content match.
>>> #
>>> #file oisfsearchnums.pcap
>>> alert tcp any any -> any any (msg:"e6504ae48c99f09df7f58996aacbb6b0 +
>>> http_cookie + byte_jump"; content:"e6504ae48c99f09df7f58996aacbb6b0";
>>> http_cookie; byte_jump:1,596,string,dec; content:"0"; distance:0;
>>> within:1; classtype:bad-unknown; sid:73; rev:1;)
>>>
>>>
>>>
>>> On Wed, Mar 10, 2010 at 4:56 PM, Will Metcalf <william.metcalf at ...3035.....> wrote:
>>>> How about this one, using the same pcap. I have both client and server
>>>> flow_depth set to 0.
>>>>
>>>> #test 72 http_cookie + byte_test.
>>>> #hmm interesting using http_cookie in combination with byte_test seems
>>>> to fail always. Removing either the byte_test check or the http_cookie
>>>> modifier will cause this sig to fire.  Notice that the byte_test
>>>> #check isn't even relative to the content match.
>>>> #
>>>> #file oisfsearchnums.pcap
>>>> alert tcp any any -> any any (msg:"e6504ae48c99f09df7f58996aacbb6b0 +
>>>> http_cookie + byte_test"; content:"e6504ae48c99f09df7f58996aacbb6b0";
>>>> http_cookie; byte_test:2,=,12,596,string,dec; classtype:bad-unknown;
>>>> sid:72; rev:1;)
>>>>
>>>>
>>>> Regards,
>>>>
>>>> Will
>>>>
>>>> On Wed, Mar 10, 2010 at 1:54 PM, Will Metcalf <william.metcalf at ...3051......> wrote:
>>>>> I can see the need for the cut-off.  You have to make compromises
>>>>> between accuracy and performance this tends to be the nature of the
>>>>> beast with IDS's,  and sure there will always be evasions abut the
>>>>> dynamic flow_depth thing still isn't making much sense to me and/or at
>>>>> least this behavior should be documented somewhere.  Did I just miss
>>>>> something in the readme?  Btw there is a typo both in the manual and
>>>>> the README regarding client_flow_depth.  "It primarily eliminates
>>>>> Snort fro inspecting larger HTTP Cookies that appear at the end of
>>>>> many client request Headers."
>>>>>
>>>>>
>>>>> Regards,
>>>>>
>>>>> Will
>>>>>
>>>>> On Wed, Mar 10, 2010 at 1:18 PM, Steven Sturges
>>>>> <steve.sturges at ...402...> wrote:
>>>>>> There are different settings for the requests & responses.
>>>>>> See client_flow_depth and server_flow_depth in the readme/manual.
>>>>>>
>>>>>> Setting either of the flow depth values to 0 would inspect
>>>>>> all of the respective request or response, but incurs a
>>>>>> pretty big performance hit.
>>>>>>
>>>>>> And yes, the default (in code) is 300 for both.
>>>>>>
>>>>>> Will Metcalf wrote:
>>>>>>> Ahhh ok so I want to make sure I understand correctly in 2.8.5 the
>>>>>>> default 300 byte cutoff is not only applied to http_responses but also
>>>>>>> http_requests (README.http_inspect) if there are http normalizations.
>>>>>>> Is there not still a potential evasion here based on the tests below
>>>>>>> as packet being normalized or potentially matching on one or more
>>>>>>> rules can be fairly unpredictable?  Would your recommended
>>>>>>> configuration then be to set client_flow_depth to 0 in the
>>>>>>> http_inspect preproc for 2.8.5 users if they wanted to avoid the
>>>>>>> potential evasion?
>>>>>>>
>>>>>>> Regards,
>>>>>>>
>>>>>>> Will
>>>>>>>
>>>>>>> On Wed, Mar 10, 2010 at 12:03 PM, Steven Sturges
>>>>>>> <steve.sturges at ...402...> wrote:
>>>>>>>> Seems that what is really coming into play is the flow depth.
>>>>>>>> That is going to limit how much of the raw data is searched
>>>>>>>> with the pattern matcher.
>>>>>>>>
>>>>>>>> To summarize how it works with 2.8.6:
>>>>>>>>
>>>>>>>> 1) If HTTP normalizes headers and cookies, the amount of raw data
>>>>>>>> searched by fast pattern matcher is determined by client (or server)
>>>>>>>> flow depth settings.
>>>>>>>>
>>>>>>>> 2) If there are no HTTP normalizations, flow depth is not applied, so
>>>>>>>> all of the raw data is searched.
>>>>>>>>
>>>>>>>> With 2.8.5, in 1) above, the flow depth was applied only if there were
>>>>>>>> rules searched for one of those HTTP normalized buffers.
>>>>>>>>
>>>>>>>> By default, client flow depth is 0 -- which is what Will is probably
>>>>>>>> hitting in his tests.
>>>>>>>>
>>>>>>>> Alerts w/ combinations of rules & different flow depths in 2.8.6:
>>>>>>>>
>>>>>>>> Default flow depth (0)
>>>>>>>> SID 59, SID 68 enabled
>>>>>>>> 1 alert (sid 59)
>>>>>>>>
>>>>>>>> Default flow depth (0)
>>>>>>>> SID 68 enabled
>>>>>>>> 0 alerts
>>>>>>>>
>>>>>>>> [Same as above for client_flow_depth 300]
>>>>>>>>
>>>>>>>> Client flow depth (1460)
>>>>>>>> SID 59, SID 68 enabled
>>>>>>>> 3 alerts (sid 59, sid 68x2)
>>>>>>>>
>>>>>>>> Client flow depth (1460)
>>>>>>>> SID 68 enabled
>>>>>>>> 2 alerts (sid 68x2)
>>>>>>>>
>>>>>>>> -steve
>>>>>>>>
>>>>>>>> Matt Jonkman wrote:
>>>>>>>>> Appreciate the clarification Steve. But I'm concerned, this will make
>>>>>>>>> hundreds if not a few thousand rules not work correctly in our set and
>>>>>>>>> in vrt/snort gpl. If someone has http_inspect on in a recent snort, but
>>>>>>>>> does NOT have ALL of their http related rules converted to the new form
>>>>>>>>> using the http_* modifiers (which we have none converted) then they're
>>>>>>>>> going to have massive problems, no? I think a lot of people are missing
>>>>>>>>> a lot of things right now.
>>>>>>>>>
>>>>>>>>> Is there a way to make http_inspect not do this? We have a lot of sigs
>>>>>>>>> that won't work on normalized data, for instance the recent trojan sigs
>>>>>>>>> that look at the order of the parameters in an http post for uniqieness.
>>>>>>>>> With the normalized only we can't see that can we?
>>>>>>>>>
>>>>>>>>> Thanks!
>>>>>>>>>
>>>>>>>>> Matt
>>>>>>>>>
>>>>>>>>> On 3/10/10 10:26 AM, Will Metcalf wrote:
>>>>>>>>>>> 1) Use http_cookie in the rule as you note in the case that works.
>>>>>>>>>> Right so the reason that I cc'd the emerging list is that they are not
>>>>>>>>>> using the http_* modifiers to maintain compatibility with older
>>>>>>>>>> versions of snort.  Shouldn't this buffer at least be available to
>>>>>>>>>> match on via rawbytes  which is what would be consistent with what you
>>>>>>>>>> have done with telnet and dcerpc.  Does this also not add a potential
>>>>>>>>>> evasion method if this is the intended behavior, one that perhaps
>>>>>>>>>> VRT/ET should be made aware of.  I haven't gone through very many of
>>>>>>>>>> the sigs but since the normalized buffer begins with the "Cookie:"
>>>>>>>>>> instead of the value isn't there a now a potential evasion if I can
>>>>>>>>>> get another sig to trip on the same packet as say sid 2136.
>>>>>>>>>>
>>>>>>>>>> Regards,
>>>>>>>>>>
>>>>>>>>>> Will
>>>>>>>>>>
>>>>>>>>>> On Wed, Mar 10, 2010 at 8:15 AM, Steven Sturges
>>>>>>>>>> <steve.sturges at ...402...> wrote:
>>>>>>>>>>> Will--
>>>>>>>>>>>
>>>>>>>>>>> In the 2nd rule the only content is an HTTP cookie.  Without using
>>>>>>>>>>> http_cookie, it would try to match the raw data.
>>>>>>>>>>>
>>>>>>>>>>> With HTTP Inspect enabled, it is separating the headers, cookie,
>>>>>>>>>>> method, etc from the raw data, hence all of the modifier keywords
>>>>>>>>>>> that you can use with content -- can use more than one together.
>>>>>>>>>>>
>>>>>>>>>>> Without specifying http_cookie in the rule and when HTTP Inspect
>>>>>>>>>>> enabled (and cookie inspection enabled in 2.8.6), if the pattern
>>>>>>>>>>> matcher searches any of the HTTP buffers, it doesn't search the raw
>>>>>>>>>>> data.  If no rules use the specific HTTP buffers or there are no HTTP
>>>>>>>>>>> buffers, the pattern matcher will search the raw data, which is why
>>>>>>>>>>> the rule byte itself (without http_cookie) works.
>>>>>>>>>>>
>>>>>>>>>>> This was done to avoid going over the same data twice in the pattern
>>>>>>>>>>> matcher, and it is working as it is designed.
>>>>>>>>>>>
>>>>>>>>>>> Two options:
>>>>>>>>>>>
>>>>>>>>>>> 1) Use http_cookie in the rule as you note in the case that works.
>>>>>>>>>>>
>>>>>>>>>>> 2) Turn off HTTP Inspect (not realistic)
>>>>>>>>>>>
>>>>>>>>>>> Cheers
>>>>>>>>>>> -steve
>>>>>>>>>>>
>>>>>>>>>>> Will Metcalf wrote:
>>>>>>>>>>>> hmmm I don't think so.  Look at first test.  both rules fire.
>>>>>>>>>>>>
>>>>>>>>>>>> Regards,
>>>>>>>>>>>>
>>>>>>>>>>>> Will
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Mar 9, 2010 at 10:31 PM, beenph <beenph at ...2499...> wrote:
>>>>>>>>>>>>> I will try a wild guess, what is your event_queue size like?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Its probably a bug or something  that need clarification regarding
>>>>>>>>>>>>> http_cookie and http_inspect, but mabey http_cookie enable a modifier
>>>>>>>>>>>>> in http_inspect that alter alerting behavior when event_queue is at 1
>>>>>>>>>>>>> (since i guess both "alerts" are part of the same normalized http
>>>>>>>>>>>>> stream)
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> -elz
>>>>>>>>>>>>> ps: didin't run the pcap and rules test.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Tue, Mar 9, 2010 at 11:15 PM, Will Metcalf <william.metcalf at ...2499...> wrote:
>>>>>>>>>>>>>> failing to use the http_cookie modifier on a rule where there is
>>>>>>>>>>>>>> another rule that matches the same packet makes a rule that should
>>>>>>>>>>>>>> fire fail.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> src/snort -V
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>   ,,_     -*> Snort! <*-
>>>>>>>>>>>>>>  o"  )~   Version 2.8.5.3 (Build 124)
>>>>>>>>>>>>>>   ''''    By Martin Roesch & The Snort Team:
>>>>>>>>>>>>>> http://www.snort.org/snort/snort-team
>>>>>>>>>>>>>>           Copyright (C) 1998-2009 Sourcefire, Inc., et al.
>>>>>>>>>>>>>>           Using PCRE version: 7.8 2008-09-05
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> src/snort -k none -q -A console -c etc/snort.conf -l ./ -r oisfsearchnums.pcap
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> #this combo works
>>>>>>>>>>>>>> #alert tcp any any -> any any (msg:"http_client_body";
>>>>>>>>>>>>>> content:"searchword="; uricontent:"/index.php"; nocase;
>>>>>>>>>>>>>> classtype:bad-unknown; sid:59; rev:1;)
>>>>>>>>>>>>>> #alert tcp any any -> any any (msg:"http_cookie match ";
>>>>>>>>>>>>>> content:"e6504ae48c99f09df7f58996aacbb6b0=120e494ce857d6ceeef89f9678d4d703";
>>>>>>>>>>>>>> http_cookie; classtype:bad-unknown; sid:68; rev:1;)
>>>>>>>>>>>>>> #
>>>>>>>>>>>>>> #03/07-21:19:54.242506  [**] [1:59:1] http_client_body [**]
>>>>>>>>>>>>>> [Classification: Potentially Bad Traffic] [Priority: 2] {TCP}
>>>>>>>>>>>>>> 192.168.100.17:38111 -> 96.43.130.5:80
>>>>>>>>>>>>>> #03/07-21:19:54.242506  [**] [1:68:1] http_cookie match  [**]
>>>>>>>>>>>>>> [Classification: Potentially Bad Traffic] [Priority: 2] {TCP}
>>>>>>>>>>>>>> 192.168.100.17:38111 -> 96.43.130.5:80
>>>>>>>>>>>>>> #03/07-21:19:54.364173  [**] [1:68:1] http_cookie match  [**]
>>>>>>>>>>>>>> [Classification: Potentially Bad Traffic] [Priority: 2] {TCP}
>>>>>>>>>>>>>> 192.168.100.17:38111 -> 96.43.130.5:80
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> #the second rule does not fire
>>>>>>>>>>>>>> #alert tcp any any -> any any (msg:"http_client_body + depth";
>>>>>>>>>>>>>> content:"searchword="; uricontent:"/index.php"; nocase;
>>>>>>>>>>>>>> classtype:bad-unknown; sid:59; rev:1;)
>>>>>>>>>>>>>> #alert tcp any any -> any any (msg:"http_cookie match";
>>>>>>>>>>>>>> content:"e6504ae48c99f09df7f58996aacbb6b0=120e494ce857d6ceeef89f9678d4d703";
>>>>>>>>>>>>>> classtype:bad-unknown; sid:68; rev:1;)
>>>>>>>>>>>>>> #
>>>>>>>>>>>>>> #03/07-21:19:54.242506  [**] [1:59:1] http_client_body + depth [**]
>>>>>>>>>>>>>> [Classification: Potentially Bad Traffic] [Priority: 2] {TCP}
>>>>>>>>>>>>>> 192.168.100.17:38111 -> 96.43.130.5:80
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> #this rule fires when used on it's own.
>>>>>>>>>>>>>> #alert tcp any any -> any any (msg:"http_cookie match";
>>>>>>>>>>>>>> content:"e6504ae48c99f09df7f58996aacbb6b0=120e494ce857d6ceeef89f9678d4d703";
>>>>>>>>>>>>>> classtype:bad-unknown; sid:68; rev:1;)
>>>>>>>>>>>>>> #
>>>>>>>>>>>>>> #03/07-21:19:54.242506  [**] [1:68:1] http_cookie match [**]
>>>>>>>>>>>>>> [Classification: Potentially Bad Traffic] [Priority: 2] {TCP}
>>>>>>>>>>>>>> 192.168.100.17:38111 -> 96.43.130.5:80
>>>>>>>>>>>>>> #03/07-21:19:54.364173  [**] [1:68:1] http_cookie match [**]
>>>>>>>>>>>>>> [Classification: Potentially Bad Traffic] [Priority: 2] {TCP}
>>>>>>>>>>>>>> 192.168.100.17:38111 -> 96.43.130.5:80
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> ------------------------------------------------------------------------------
>>>>>>>>>>>>>> Download Intel® Parallel Studio Eval
>>>>>>>>>>>>>> Try the new software tools for yourself. Speed compiling, find bugs
>>>>>>>>>>>>>> proactively, and fine-tune applications for parallel performance.
>>>>>>>>>>>>>> See why Intel Parallel Studio got high marks during beta.
>>>>>>>>>>>>>> http://p.sf.net/sfu/intel-sw-dev
>>>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>>>> Snort-devel mailing list
>>>>>>>>>>>>>> Snort-devel at lists.sourceforge.net
>>>>>>>>>>>>>> https://lists.sourceforge.net/lists/listinfo/snort-devel
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>> ------------------------------------------------------------------------------
>>>>>>>>>>>> Download Intel® Parallel Studio Eval
>>>>>>>>>>>> Try the new software tools for yourself. Speed compiling, find bugs
>>>>>>>>>>>> proactively, and fine-tune applications for parallel performance.
>>>>>>>>>>>> See why Intel Parallel Studio got high marks during beta.
>>>>>>>>>>>> http://p.sf.net/sfu/intel-sw-dev
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> Snort-devel mailing list
>>>>>>>>>>>> Snort-devel at lists.sourceforge.net
>>>>>>>>>>>> https://lists.sourceforge.net/lists/listinfo/snort-devel
>>>>>>>>>>>>
>>>>>>>>>> ------------------------------------------------------------------------------
>>>>>>>>>> Download Intel® Parallel Studio Eval
>>>>>>>>>> Try the new software tools for yourself. Speed compiling, find bugs
>>>>>>>>>> proactively, and fine-tune applications for parallel performance.
>>>>>>>>>> See why Intel Parallel Studio got high marks during beta.
>>>>>>>>>> http://p.sf.net/sfu/intel-sw-dev
>>>>>>>>>> _______________________________________________
>>>>>>>>>> Snort-devel mailing list
>>>>>>>>>> Snort-devel at lists.sourceforge.net
>>>>>>>>>> https://lists.sourceforge.net/lists/listinfo/snort-devel
>>
>




More information about the Snort-devel mailing list