[Oisf-users] real time alert on tcp stream and flowint
Nikolay Denev
ndenev at gmail.com
Sat Feb 11 19:27:00 UTC 2012
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;)
>>>
>>>
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>>>
>>>
>>> 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
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