[Snort-devel] BUG: corner case involving http_cookie

Will Metcalf william.metcalf at ...2499...
Wed Mar 10 10:26:19 EST 2010


> 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 ...3035.....> 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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