[Snort-users] help writing snort rule

Joel Esler joel.esler at ...1935...
Fri Jan 26 14:31:07 EST 2007


Bill,

This is exactly the correct place to ask Snort Rules questions.

I suggest you eliminate the "ip" in the rule.  Try replacing it with  
TCP or even using the tcp rule that I jotted down.

Grabbing it out of an email should be easy, however an attachement is  
not so easy depending upon the type of attachment, for example, if  
it's a plaintext document or something, yes, it might grab it, but if  
it's written in Word, or maybe a pdf, since those are formatted  
differently, it's a bit harder.

So, step one, lets move from ip to tcp, and see how that works.   
Also, try and eliminate your any any, perhaps change it to any any to  
HOME_NET any

J

On Jan 26, 2007, at 1:58 PM, Bill Lopez wrote:

> Thank you for the quick response to my question.
>
>
>
> I don’t want to keep asking elementary questions in this forum if  
> its not appropriate, please let me know if this isn’t the proper  
> place and direct me to where I can ask basic questions.
>
>
>
> I wasn’t able to get an alert on the bleeding rule
>
>
>
> alert tcp any any -> any any (msg: "BLEEDING-EDGE SSN Detected in  
> Clear Text"; flow: established; pcre:"/ ([0-6]\d\d|7[0-256]\d|73 
> [0-3]|77[0-2])-\d{2}-\d{4} /"; classtype: policy-violation; sid:  
> 2001328; rev:8; )
>
>
> thus the reason for trying to write my own with a small variance in  
> the character string –
>
>
>
> alert ip any any -> $EXTERNAL_NET any (pcre:"/\d{3}(\s|-)?\d{2} 
> (\s|-)?\d{4}/"; msg:"SSN Detected in Clear Text"; sid: 1000004;)
>
>
>
> which doesn’t produce an alert either – eventually I want to apply  
> this filter to just traffic from/to mail , telnet, ftp (etc)  
> servers – I can send any variance of xxx-xx-xxxx, xxxxxxxx  or xxx  
> xx xxxx via an e-mail, text file attachment or file upload and  
> still never see an alert to the console.  I have a simple rule to  
> check for content using a keyword and get alerted when sending that  
> keyword with e-mail, attachment and file upload (this was my test  
> to see if snort was actually alerting correctly)  I am only running  
> my test rules with an out of the box snort.conf file.
>
>
>
> Why wouldn’t either of the above rules alert with (for example) an  
> e-mail sent with 555-55-5555 in the body?
>
>
>
>
>
> Bill Lopez
>
> Operating Engineers Trust Funds
>
> (626) 356-3524
>
> (626) 255-1066
>
>
>
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--Joel
joel.esler at ...1935...
http://demo.sourcefire.com/jesler.pgp.key





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