[Snort-users] Problems on Flowbits Option

Luo Xin kingsleyluoxin at ...125...
Tue Apr 11 23:33:05 EDT 2017


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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