Hi Dwane,
There is a problem with this rule. The content detection portion of the rule
looks good, it looks for the 530 response from FTP for an incorrect login.
The problem lies within the rule header though (alert tcp $HOME_NET any ->
$EXTERNAL_NET 21), this content that is being looked for is from the client to
the server, where it is really the server that sends the 530 error code so by
switching the direction your monitoring this pattern for you should be good to
go (alert tcp $EXTERNAL_NET 21 -> $HOME_NET any).
//Joel
StillSecure
Joel Ebrahimi
Senior Software Engineer
http://www.stillsecure.com/
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-----Original Message-----
From: snort-users-bounces@lists.sourceforge.net on behalf of Atkins, Dwane P
Sent: Wed 6/27/2007 9:18 AM
To: Snort-users@lists.sourceforge.net
Subject: [Snort-users] Rules to block FT
I have a testbed set up and have already alerted and blocked via
snortsam for SSH. I am now working on FTP.
My rule:
alert tcp $HOME_NET any -> $EXTERNAL_NET 21 ( msg:"BLOCKED Potential
FTP Brute-Force attempt";flow:from_server,established; content:"530 ";
pcre:"/^530\s+(Login|User|Failed)/smi";classtype:unsuccessful-user;
threshold: type threshold, track by_dst, count 10, seconds 60;
sid:1000002; rev:1; fwsam: src, 5 minutes;)
Does this look like it will work? I am not that adept about building
rules and am learning. This was from bleeding edge, I think.
Dwane
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