[Snort-devel] BUG: corner case involving http_cookie

Will Metcalf william.metcalf at ...2499...
Mon Mar 15 10:34:13 EDT 2010


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 ...2499...> 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 ...3054....> 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
>>>>>>>>>>>>
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