[Snort-users] Multiple Content (not working?)

F.M. Taylor root at ...28...
Wed May 15 13:03:04 EDT 2002


Another thing that should be considered.  <voice of experience> Even when
FlexResp is working properly against an SMTP server all it does is drop
the connection at which time the MTA on their end simply tries again,
eating up your CPU and bandwidth.  You are only delaying the inevitable.  
</voe>

On Wed, 15 May 2002, Matt Kettler wrote:

> Hmm, as a bit of a side note, this sounds more like a job better fixed by 
> configuring your mailserver's access rules or using procmail than using snort.
> 
> Also of note, Flexresp is *NOT* a sure thing and you should NEVER count on 
> it as a primary line of preventing a known attack. EVER. No, really, if 
> you're relying on flexresp to stop traffic you don't want you're going to 
> have it fail sooner or later. It's more of a last-ditch effort to stop an 
> attack that you did not know was possible on your network. It only really 
> has a chance of working due to network latencies, and a deliberate attacker 
> can fire off a second packet right behind the offending one to advance the 
> sequence number and likely do so before snort can respond.
> 
> At any rate, given normal SMTP transactions the from and to lines are not 
> likely to be in the same TCP segment, since the server has to reply after 
> the "MAIL FROM" command and the "RCPT TO" command. Hence your pass rule 
> will not likely ever trigger in reality, unless the person delivering mail 
> to your server is not SMTP compliant and is just firing off commands 
> without waiting for acknowledgement from the server.
> 
> 
> 
> At 05:26 AM 5/15/2002 -0300, you wrote:
> >Hello,
> >
> >I'm with some problems here while trying to configure
> >multiple content options to a rule.
> >
> >I need to block a unique e-mail address to send messages
> >to all my users, but this messages can be posted to me.
> >
> >well... I've tried two rules:
> >pass tcp $SMTPX any -> $MYSMTP 25
> >(content:"that at ...1266...";nocase;content:"my at ...1266...";n
> >ocase;)
> >alert tcp $SMTPX any -> $MYSMTP 25
> >(content:"that at ...1266...";nocase;resp:rst_all;)
> >
> >May anyone help me to this work? plz!
> >I've lost some nights trying to figure out what's wrong.
> >
> >Thanks in advance.
> >
> >
> >Best Regards
> >__________________
> >Carlos Kumbak
> >ckumbak at ...1331...
> >
> >
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-- 
Mike Taylor
Coordinator of Systems Administration and Network Security
Indiana State University.               Rankin Hall Rm 053
210 N 7th St.                           Terre Haute, IN.
SANS GSEC  http://www.sans.org/





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