[Snort-sigs] Bleeding addition

James Ashton James at ...2424...
Mon Jun 28 13:44:07 EDT 2004


I would say that, depending on your network layout, you could also be
worried about internal machines sending mail to other internal machines.
This can be as bad as traffic coming and going to the net at large.

There are SO many network layouts that this rule makes sense in many and
not in some of the more standard ones...  But when was the last time you
had trouble with perimeter security in a standard network layout.......


James Ashton
http://bleedingsnort.com
http://www.gitflorida.com

-----Original Message-----
From: snort-sigs-admin at lists.sourceforge.net
[mailto:snort-sigs-admin at lists.sourceforge.net] On Behalf Of Adrian
Marsden
Sent: Monday, June 28, 2004 3:29 PM
To: Matthew Jonkman
Cc: snort-sigs mailinglist
Subject: RE: [Snort-sigs] Bleeding addition

It makes sense up to the point you say that you are looking to detect
what slips through. If the firewall is configured to deny out SMTP then
nothing should be slipping through. My firewalls block all outbound
except from my mail servers and drops an alert to my desktop if any
machine tries. I can see the point of a Snort rule if your firewall
can't alert the admin, other than that the Snort rule would be somewhat
redundant other than for logging purposes since the firewall will have
already logged it for you when it alerted you. Or am I missing something
here?



-----Original Message-----
From: Matthew Jonkman [mailto:matt at ...2436...] 
Sent: Monday, June 28, 2004 2:47 PM
To: Adrian Marsden
Cc: snort-sigs mailinglist
Subject: Re: [Snort-sigs] Bleeding addition

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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-- 
--------------------------------------------
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Senior Security Engineer
Infotex
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765-448-6847 Office
866-679-5177 24x7 NOC
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