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Network Security Snort-Signatures
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Re: [Snort-sigs] rule with traffic in both directions

from [Brian] Network Security [Permanent Link]
Subject: Re: [Snort-sigs] rule with traffic in both directions
Date: Mon, 25 Apr 2005 10:48:06 -0400 
On Sat, Apr 23, 2005 at 11:08:05PM +0200, hans wrote:

tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"SMTP RSET";
flow:to_server,established; content:"rset"; nocase;
pcre:"/^rset/smi"; classtype:attempted-recon; sid:050313; rev:1; )

now i would like to modify this. it should only fire, if in the
traffic some packets bevor, in direction from server to client
the following text "Greylisting in action" as part 
of the stream can be found. 



alert tcp $SMTP_SERVERS 25 -> EXTERNAL_NET (msg:"SMTP GREYLIST";
    flow:from_server,established; content:"Greylisting in action"; nocase;
    flowbits:set,smtp.greylist;)
alert tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"SMTP RSET";
    flow:to_server,established; flowbits:isset,smtp.greylist;
    content:"rset"; nocase; pcre:"/^rset/smi";)

Brian


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