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From: Aaron Turner (aturner_at_pobox.com)
Date: Tue Oct 29 2002 - 11:02:57 CST
On Tue, Oct 29, 2002 at 09:28:08AM -0500, Matt Harris wrote:
> Aaron Turner wrote:
> > 1) Futzing with router ACL's or firewall policies via your IDS is not granular.
> > They don't drop a specific connection (the attack) but rather all traffic on
> > a given port for a client/server. This can have very ugly effects for
> > legit traffic.
> Generally, this is done on a basis of simply blocking all inbound
> traffic from the offender's IP address. Hence entirely blocking the
> effective attack as well as anything else they may try for the next X
> number of seconds/minutes/whatever.
That's exactly what you shouldn't be doing. Let's say you detect someone
attacking your network. How do you know:
1) That the packets don't have a forged source IP?
2) The the user isn't behind some HTTP, socks, etc proxy?
Either case and you've likely killed perfectly legit traffic while
stopping the attack, perhaps preventing paying customers from doing
business with you. Things like port scans and DoS attacks very often
include packets with forged source IP's.
> > 2) It's too late. The attack has already reached the target. Consider
> > something like jill.c which exploits the IIS-ISAPI buffer overflow and
> > opens a connection back to the attacker on another port and you'll quickly
> > understand why this method of "protection" is more hype than reality.
> If people are running insecure web servers, then is it really the
> network infrastructure's job to protect them?
I've never met any admin of any OS (Solaris, Linux, Windows mostly) who
claimed that he/she had patched all of the servers within 24 hours of a
patch on a regular basis. Most wouldn't even claim 7 days or even a few
weeks. Is this best-practices? Not even close. Is it the reality?
Absolutely, especially since most companies don't have their IT group
fully staffed due to the economy.
When you consider most (all??) worms effecting IIS were exploiting
bugs which had patches released months in advance, it's clear to me at least
that companies are either unwilling or unable to keep up. Hence, it seems
reasonable that the market will come up with an alternative solution which
requires less effort on the admin. (Assuming they don't all move their
servers to OpenBSD :-)
> I'm thinking more along
> the lines of protecting against flood attacks, port scans, and the like
> - from smurfs to simple icmp floods, etc. In addition, blocking at the
> border router level can be even more useful for this, since it stops it
> before it gets to the IDS, Firewall, etc, and hence saves them some
> processing time for legitamate traffic. It's not a perfect solution to
> all problems, but IMO the only real solution has to be at every level -
> I only go so far with network based security, and rely on host based
> security for the rest. Exploits just shouldn't work against systems,
> and if they do because some admin was lazy, then it shouldn't be my
> IDS's job to protect their lazy selves. ;-)
While I want to agree with you (there's something nice in the thought that
only lazy admins get their servers broken into), in reality it's not a
question of laziness. Generally I see a few major issues:
1) Just not enough people to do all the work. The economic downturn makes
this even worse than it was with many companies laying people off or
imposing hiring freezes.
2) Too many patches and severs to keep up with. Just trying to keep
up with all the security patches that the vendors keep spewing is insane.
3) Also, some very popular vendors *cough*MicroSoft*cough* like to
downplay the vulnerability to save face, so admins even if they are trying
to keep up tend to prioritize patches poorly.
4) Patching systems often cause downtime. Hence, it often requires the
work to be done during non-peak hours (late at night). IT people,
contrary to popular belief do occasionally have a life/family and can't be
doing patches 7 nights a week (assuming their windows would even allow that).
5) Plain ignorance and/or laziness. Yes, some admins think it'll never
happen to them and that nobody would ever target them. We all know
they're wrong, and get pissed off when it's now their servers attacking us.
> Security is everyone's concern. If it isn't a particular person's
> concern, then they'll be the ones to have to fix or rebuild their
Yep. Of course as many people have been arguing, security should be
done in depth. I'm not saying an NIPS can prevent all attacks
so you don't have to ever patch your systems again. That's insane.
I tend to think of inline NIPS as a lifejacket. If you're smart and pay
attention, you really shouldn't ever need it. But if something bad
happens, it's a real good thing to have. And of course, if you're
really stupid or just unlucky, even a lifejacket won't save you.
> But that's a philosophical and business difference for a lot of people.
> I'm in a place where business decisions don't affect things since we're
> not running a business. And as far as philosophy, see above.
Consider yourself lucky then! Not many of us can say that business decisions
don't effct our work.
> > 3) Many attacks are internal. Most firewalls are at the border, hence
> > there's nothing the firewall can do, unless you (re)deploy more firewalls.
> True enough. Deploying internal firewalls and IDS's is definitly not a
> bad thing, if not in fact even a good thing. Most of the attacks I see
> internal are unintentional user-mishaps, I've yet to see any genuine
> malicious activity. But nonetheless, we try to be prepared.
> Statistically here, about 99% of attacks outside of individual subnets
> (I have no way of monitoring what may go on within a seperate subnet,
> though I think the help desk would be getting calls if something bad
> happened that affected users adversely), come from the internet. So,
> that is where the effort here is in fact concentrated.
Expecting your help desk to notice/get calls is a big if. An obvious
example was the latest attack on the root name servers. Definaltely
an attack, just most people didn't happen to notice. The root
name servers are closely monitored by the admins of course, so they
knew even if the users didn't.
Consider the IIS-ISAPI exploit again... since IIS restarts after it crashes
unless someone was paying attention to the logs (or had an IDS) one would
generally not realize they had been broken into.
-- Aaron Turner <aturner at pobox.com|synfin.net> http://synfin.net/aturner They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety. -- Benjamin Franklin
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