Re: on TASL correlation rules

["rgula () tenablesecurity com" <rgula () tenablesecurity com>]

I think a lot of this goes to the level of maturity an
organization has. If they are the wild west with no idea
what is on their network, it's hard to figure out what
is expected behavior and then look for deviations from this.
On the other hand, if exact details of who should be talking
to who are known, exceptions to this can find intruders and
folks behaving poorly. 
 
This is one of the main reasons Tenable is in both the 
vulnerability and security event management businesses as I
feel they are completely tied at the hip.  
 
If folks want to read more on this type of approach, they 
should check out Tenable's "Network Security Implications 
of 'Visible Ops'" paper at:
 
http://www.tenablesecurity.com/whitepapers/compliance.shtml
 
This discusses how SIM, VA, passive monitoring, .etc can
help
move an organization from an un-managed to managed state.

Tactically, an organization using all of Tenable's products 
can monitor which assets communicate with each other and
easily
write TASL scripts to look for activity outside of those
ranges.
These relations can come from passive sniffing, netflow and 
log analysis.

For example, our NeVO sensor can sniff traffic to/from your
DMZ
and find the SSH, SNMP, .etc command channels. This info can
be
used to edit one of our exisitng TASL scripts to modify it
to 
alert if an SSH connection occurs outside of the expected 
behavior. 
 
Ron Gula, CTO
Tenable Network Security
 
----- Original Message -----
From: Anton Chuvakin <anton () chuvakin org>
To: Ron Gula <rgula () tenablesecurity com>
Cc: focus-ids () securityfocus com
Subject: Re: on TASL correlation rules
Date: Fri, 23 Dec 2005 17:03:13 -0500
 
> Ron and all,
>
> > In general though, the issue we've found while writing
> > these types of rules is that whatever the algorithm,
> > there is always a trade off between being exact and
> being general. That is *exactly* the discussion I wanted
> to start! Thanks for picking it up. When one provides
> canned correlation rules (such as your TASL scripts), this
> question comes up in full force. And, unlike NIDS rules,
> where people expect them to work pretty much out of the
> box (I think its a dirty little secret that much fewer
> customers customize NIDS rules than the NIDS vendors
> think...), this one gets real subjective real quick.  And
> this is where the site-specific rules or scripts come in.
>
> > Site-specific rules can get much more interesting. For
> > example, writing a rule that can alert on any "SSH login
> > failure" not coming from the SOC is very simple, but you
> > have to know about the DNS server, the SOC and the trust
> relationship between them before hand. This is one of my
> favorite examples: its an extremely simple and just as
> useful custom rule ("if SSH not from SOC, alert") but an
> impossible default vendor -provided rule.  The main
> question is: how many people will go and create it? Will
> the "NIDS disease" (mentioned above) hit it as well and
> thus devalue the correlation software?
>
> Best,
> --
> Anton Chuvakin, Ph.D., GCIA, GCIH, GCFA
>      http://www.chuvakin.org
>  http://www.securitywarrior.com
>
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