[Oisf-users] real time alert on tcp stream and flowint
Nikolay Denev
ndenev at gmail.com
Sun Feb 12 07:15:46 UTC 2012
On Feb 11, 2012, at 10:11 PM, Peter Manev wrote:
>
>
> On Sat, Feb 11, 2012 at 8:27 PM, Nikolay Denev <ndenev at gmail.com> wrote:
>
> On Feb 11, 2012, at 9:14 PM, Peter Manev wrote:
>
>>
>>
>> On Sat, Feb 11, 2012 at 7:42 PM, Nikolay Denev <ndenev at gmail.com> wrote:
>>
>> On Feb 11, 2012, at 7:52 PM, Peter Manev wrote:
>>
>>>
>>>
>>> On Sat, Feb 11, 2012 at 4:31 PM, Nikolay Denev <ndenev at gmail.com> wrote:
>>>
>>> On Feb 11, 2012, at 12:11 PM, Peter Manev wrote:
>>>
>>>>
>>>>
>>>> On Fri, Feb 10, 2012 at 6:43 AM, Nikolay Denev <ndenev at gmail.com> wrote:
>>>>
>>>> On Feb 9, 2012, at 10:04 PM, Nikolay Denev wrote:
>>>>
>>>> > On Feb 9, 2012, at 10:03 PM, Nikolay Denev wrote:
>>>> >
>>>> >> Hi all,
>>>> >>
>>>> >> It's probably stupid question and I'm missing something but I don't seem to be able
>>>> >> to generate alert immediately when for example a given string is found inside a TCP stream.
>>>> >> When the TCP connection closes, suricata immediately prints the alert in fast.log.
>>>> >> How can I make the alert be generated immediately when the rule condition is matched?
>>>> >>
>>>> >> Also I don't know if its because of this I don't seem to be able to trigger the rule to match several times on the same stream,
>>>> >> while I have the string that should fire the alert several times in the stream.
>>>> >>
>>>> >> Here's an example :
>>>> >>
>>>> >> alert tcp $HOME_NET 6666 -> any any \
>>>> >> (msg:"got one"; content:"something"; flowint:something,notset; flowint:something,=,1; sid:10;)
>>>> >>
>>>> >> alert tcp $HOME_NET 6666 -> any any \
>>>> >> (msg:"got five or more"; content:"something"; flowint:something,isset; flowint:something,+,1; flowint:something,>,5; sid:11;)
>>>> >>
>>>> >> This never works, I just have the first rule fire once when the TCP session is terminated.
>>>> >>
>>>> >>
>>>> >> P.S.: As a side note the wiki should be updated to include probably "sid"s for the rules, as currently when I try to run the examples
>>>> >> suricata complains about duplicated rules.
>>>> >>
>>>> >> Thanks,
>>>> >>
>>>> >
>>>> > I'm running 1.2.1 RELEASE on FreeBSD-9.0-STABLE.
>>>>
>>>> This seems to work :
>>>>
>>>> alert tcp $HOME_NET 6666 -> any any \
>>>> (msg:"got one"; content:"something"; flowint:something,notset; flowint:something,=,1; noalert; sid:10; priority: 1;)
>>>>
>>>> alert tcp $HOME_NET 6666 -> any any \
>>>> (msg:"got more"; content:"something"; flowint:something,isset; flowint:something,+,1; noalert; sid:11; priority: 2;)
>>>>
>>>> alert tcp $HOME_NET 6666 -> any any \
>>>> (msg:"got too many"; content:"something"; flowint:something,isset; flowint:something,>,2; sid:12; priority: 3;)
>>>>
>>>>
>>>> _______________________________________________
>>>> Oisf-users mailing list
>>>> Oisf-users at openinfosecfoundation.org
>>>> http://lists.openinfosecfoundation.org/mailman/listinfo/oisf-users
>>>>
>>>>
>>>> Hi Nikolay,
>>>> I think this is the way it is supposed to work. (last example, by you).
>>>>
>>>> When you take out "noalert" form sid 11 - does it fire ?
>>>>
>>>> And are these the only rules that are loaded in terms of flowint or you have others before that?
>>>>
>>>> thanks
>>>>
>>>>
>>>>
>>>> --
>>>> Peter Manev
>>>
>>>
>>> Yes, It fires, the problem I have is that it doesn't fire for each occurence of "content".
>>> Is alert supposed to fire once per packet if it matches, or for each match in the stream?
>>>
>>> For example now I'm using these rules to catch if there are more than some defined amount of email addresses in a given stream :
>>>
>>>
>>> alert tcp $HOME_NET 80 -> any any \
>>> (msg:"got one email addr"; content:"|40|"; pcre:"/[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}/i"; \
>>> flow:established,from_server; flowint:something,notset; flowint:something,=,1; sid:10; priority:3; noalert;)
>>>
>>> alert tcp $HOME_NET 80 -> any any \
>>> (msg:"got more email addrs"; content:"|40|"; pcre:"/[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}/i"; \
>>> flow:established,from_server; flowint:something,isset; flowint:something,+,1; sid:11; priority:2; noalert;)
>>>
>>> alert tcp $HOME_NET 80 -> any any \
>>> (msg:"Got too many email addrs!"; content:"|40|"; pcre:"/[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}/i"; \
>>> flow:established,from_server; flowint:something,isset; flowint:something,>,10; sid:12; priority:1; classtype:policy-violation;)
>>>
>>>
>>> This for example works, but would not match for a simple plain text file with 10 email adresses, I need to have maybe 40-50 or more for this to match.
>>> Maybe I'm missing something…
>>> And yes, these are my only rules that I'm testing with. No other rules with or without flowint whatsoever.
>>>
>>>
>>> Hi ,
>>> Just so I understand you correctly - you have a text file (in the stream) and in that text file you have 10 e-mail addresses and it wold not fire. correct ?
>>>
>>>
>>> thanks
>>>
>>>
>>> --
>>> Peter Manev
>>
>> Exactly.
>>
>> For example if I try to fetch the file emails.txt via http which has the following content :
>>
>> # cat emails.txt
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>>
>> $ curl http://testserver/emails.txt
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> edin at email.com
>> $
>>
>> And I also remove the "noalert" option from the rules, this is what I get in fast.log :
>>
>> 02/11/2012-20:37:23.988271 [**] [1:10:0] got one email addr [**] [Classification: (null)] [Priority: 3] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:57923
>> 02/11/2012-20:37:23.988271 [**] [1:11:0] got more email addrs [**] [Classification: (null)] [Priority: 2] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:57923
>>
>>
>> If I change the third rule to fire if the flowint var is more than 1, it is being triggered.
>>
>> If I insert some random data between the email addresses in the text file, then I get 4 maybe 5 matches. Doesn't it have to match all 10 of them?
>>
>> 1. What happens if you take out the PCRE expressions from all the rules ?
>> 2. sid:12 - should not fire because you have >10 , and there are exactly 10 e-mails in the file
>> 3. how big is the stream itself? i think it is below 2KB, correct?
>> 4. is the PCRE matching the e-mails, under the unix shell ?
>> 5. yes i think you should get more sid:11 alerts - but first lets investigate the above 4.
>>
>> thanks
>>
>> --
>> Peter Manev
>
> The file with only the 10 emails is 160 bytes. Even without pcre I get the same result :
>
> alert tcp $HOME_NET 80 -> any any \
> (msg:"got one email addr"; content:"|40|"; \
> flow:established,from_server; flowint:something,notset; flowint:something,=,1; sid:10; priority:3;)
>
> alert tcp $HOME_NET 80 -> any any \
> (msg:"got more email addrs"; content:"|40|"; \
> flow:established,from_server; flowint:something,isset; flowint:something,+,1; sid:11; priority:2;)
>
> alert tcp $HOME_NET 80 -> any any \
> (msg:"Got too many email addrs!"; content:"|40|"; \
> flow:established,from_server; flowint:something,isset; flowint:something,>,9; sid:12; priority:1; classtype:policy-violation;)
>
>
> alerts I get :
>
> 02/11/2012-21:23:14.567194 [**] [1:10:0] got one email addr [**] [Classification: (null)] [Priority: 3] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:58158
> 02/11/2012-21:23:14.567194 [**] [1:11:0] got more email addrs [**] [Classification: (null)] [Priority: 2] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:58158
>
> If I put some '#' symbols between the emails in the file so that it gets about 9K big and I fetch it I get these alerts :
>
> 02/11/2012-21:25:37.755214 [**] [1:10:0] got one email addr [**] [Classification: (null)] [Priority: 3] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:58166
> 02/11/2012-21:25:37.755214 [**] [1:11:0] got more email addrs [**] [Classification: (null)] [Priority: 2] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:58166
> 02/11/2012-21:25:37.761077 [**] [1:11:0] got more email addrs [**] [Classification: (null)] [Priority: 2] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:58166
> 02/11/2012-21:25:37.764451 [**] [1:11:0] got more email addrs [**] [Classification: (null)] [Priority: 2] {TCP} X.X.X.X:80 -> Y.Y.Y.Y:58166
>
>
>
> Hi Nikolay,
>
>
> Can you please post this as a bug - please be detailed (as you were in your 2 previous e-mails).
> Personally i think here sid 11 is the problem , may be it does not count/increment correctly....
> thanks
>
>
> --
> Peter Manev
Yes I will post this as a bug. But I've just found a much simpler case.
Let's for example have only this rule in suricata :
alert tcp $HOME_NET 6666 -> any any (msg:"match"; content:"|40|";)
Then on a monitored machine from the $HOME_NET range I do :
echo "@ @ @ @ @ @ @ @ @" | nc -l 6666
And on different host I do :
nc testserver 6666
This gets the ten @ chars transferred, and I get only one alert.
But for example if I echo more @ chars, like 5000 or something, I get 3-6 alerts.
I have to check what is actually the number of packets with payload, probably the rule
is matched once per packet? But this could not explain that I get different number of alerts on different runs.
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