[Snort-users] Problems on Flowbits Option

Joel Esler (jesler) jesler at ...589...
Wed Apr 12 20:33:49 EDT 2017


Oh I'm sorry I didn't see what you did there.  I don't think you set and track flowbits on just flags, as there's no flow established on the three way handshake yet.  

--
Sent from my iPhone

> On Apr 12, 2017, at 20:25, Luo Xin <kingsleyluoxin at ...125...> wrote:
> 
> Thank you for taking time to reply!
> In fact, I think I have set the states S1, S2 and S3. Are those wrong use of flowbits? I have actually been desired to track the states of protocol and detect some anomaly behaviors.  
> 
> 在 2017/4/12 下午7:16,“Joel Esler (jesler)”<jesler at ...589...> 写入:
> 
>    I don't see anywhere where you are "set" ting a flowbit.   So you aren't tracking anything.   That's why you are getting the result you want.  
> 
>    --
>    Sent from my iPhone
> 
>> On Apr 11, 2017, at 23:35, Luo Xin <kingsleyluoxin at ...125...> wrote:
>> 
>> alert tcp any any -> $HOME_NET any (msg: "State 1"; GID: 1; sid: 10000001; flags: S; flowbits: isnotset, S1; flowbits: set, S1;)
>> alert tcp $HOME_NET any -> any any (msg: "State 2"; GID: 1; sid: 10000002; flags: SA; flowbits: isset, S1; flowbits: set, S2;)
>> alert tcp any any -> $HOME_NET any (msg: "State 3"; GID: 1; sid: 10000003; flags: A; flowbits: isset, S2; flowbits: set, S3;)
>> 
>> My rules are something like this, and I hope to use this to detect syn flooding attacks. So how is it possible to describe the situation that is not accepted by the state machine?
>> 
>> 在 2017/4/12 上午10:25,“Al Lewis (allewi)”<allewi at ...589...> 写入:
>> 
>>   It will help if you provided an example. 
>> 
>>   “My rules don’t work” isnt much to go on :-)
>> 
>> 
>>   Albert Lewis
>>   ENGINEER.SOFTWARE ENGINEERING
>>   SOURCEfire, Inc. now part of Cisco
>>   Email: allewi at ...589... 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>>>   On 4/11/17, 9:58 PM, "Luo Xin" <kingsleyluoxin at ...125...> wrote:
>>> 
>>> 
>>> 
>>> I am trying to build a state machine for TCP or other protocols. But I don’t know why my rules donn’t work. ☹
>>> 
>>> 发件人: "Joel Esler (jesler)" <jesler at ...589...<mailto:jesler at ...589...>>
>>> 日期: 2017年4月10日 星期一 下午11:55
>>> 至: Luo Xin <kingsleyluoxin at ...125...<mailto:kingsleyluoxin at ...125...>>
>>> 抄送: "snort-users at lists.sourceforge.net<mailto:snort-users at lists.sourceforge.net>" <snort-users at lists.sourceforge.net<mailto:snort-users at lists.sourceforge.net>>
>>> 主题: Re: [Snort-users] Problems on Flowbits Option
>>> 
>>> Many people have done what you are trying to do.  What are you trying to do??
>>> 
>>> 
>>> --
>>> Joel Esler | Talos: Manager | jesler at ...589...<mailto:jesler at ...589...>
>>> 
>>> 
>>> 
>>> 
>>> 
>>> On Apr 10, 2017, at 3:55 AM, Luo Xin <kingsleyluoxin at ...125...<mailto:kingsleyluoxin at ...125...>> wrote:
>>> 
>>> Hello, everyone!
>>> 
>>> 
>>> I have been confused about the flowbits option. According to the snort manual, it is possible to use this option to implement a simple state machine. I have been trying to do that, but my tries prove to be failure. I have been wondering if I have wrong understanding about this flowbits option.
>>> 
>>> 
>>> Is there anybody that has ever used flowbits option to implement a protocol state machine? If any, would you please be so kind as to help me solve my puzzles?
>>> 
>>> 
>>> Any help shall be appreciated .
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>> 
>> 
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