[Snort-sigs] Bleeding addition

Matthew Jonkman matt at ...2436...
Mon Jun 28 11:48:01 EDT 2004


I agree that prevention is the best case, and we recommend our clients 
do so, and help them do it.

But security is about layers. I'm looking to detect what slips through. 
In most nets it'd be stopped at the firewall, but we'd still see the 
infected host try to initiate a connection.

That make sense?

Matt

Adrian Marsden wrote:

> If you are looking for outbound SMTP then the probability is high that
> you only want your mail servers sending out email.
> 
> The easy way to do that is to prevent all outbound access on port 25 at
> the firewall except for the mail servers themselves. In that way the
> virus does not get propagated and you get warned by the firewall logs of
> which machines have a virus with it's own SMTP engine, (which is almost
> every one).
> 
> Much easier and more efficient than writing rules to catch unauthorized
> traffic then have to go chasing it down after the fact. If it's
> unauthorized and you can prevent it, prevent it first if at all
> possible.
> 
> -----Original Message-----
> From: Brian [mailto:bmc at ...95...] 
> Sent: Monday, June 28, 2004 1:21 PM
> To: Matthew Jonkman
> Cc: snort-sigs mailinglist
> Subject: Re: [Snort-sigs] Bleeding addition
> 
> On Mon, Jun 28, 2004 at 11:38:54AM -0500, Matthew Jonkman wrote:
> 
>>What they'll do is help you find infected hosts. It's been working
> 
> very 
> 
>>well for us for some time. You can generally narrow down the hosts
> 
> that 
> 
>>should be sending mail to 5 or 10, these sigs will tell you where they
> 
> 
>>are quickly, then add them to the SMTP_SERVERS var. Lots of good info 
>>will come from these. We've also caught a few vendors sending 
>>'anonymous' system information without our awareness. :)
>>
>>pass tcp $SMTP_SERVERS any -> any 25 ( sid:2000324; rev: 1; 
>>msg:"BLEEDING-EDGE Ignore Authorized SMTP Traffic";)
>>pass tcp any any -> $SMTP_SERVERS 25 ( sid:2000325; rev: 1; 
>>msg:"BLEEDING-EDGE Ignore Authorized SMTP Traffic";)
>>alert tcp !$SMTP_SERVERS any -> any 25 ( sid:2000326; rev: 1; 
>>msg:"BLEEDING-EDGE Possible UnAuthorized SMTP Traffic"; content:"RCPT 
>>TO"; nocase;)
>>
>>Again, these are in stable-side for now, they'll go into the 
>>bleeding.rules in a few days.
> 
> 
> In the process of doing this detection, you have invalidated ALL of
> the SMTP rules currently in the system.  Hopefully nobody running
> these rules care about attacks on their real mail servers.
> 
> Brian
> 
> 
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-- 
--------------------------------------------
Matthew Jonkman, CISSP
Senior Security Engineer
Infotex
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