North American Network Operators Group

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Re: zotob - blocking tcp/445

  • From: Christopher L. Morrow
  • Date: Tue Aug 16 00:50:25 2005

On Tue, 16 Aug 2005, Gadi Evron wrote:
> Randy Bush wrote:
> >>>>I'm not nearly confident enough to decide on behalf of almost
> >>>>billion other people how they should benefit from the Internet
> >>>>and how not to.
> >>>
> >>>thanks for that!
> >>
> >>Indeed.  Also see
> >>
> >
> >
> > as i just replied to a private message from an enterprise op,
> >
> >   o backbone isps can not set their customers' security policy
> >     - some customers want to run billyware shares over the wan
> >       whether we advise it or not
> >     - some of us host security researchers, who have a taste
> >       for 445 and other nasty traffic
> >
> >   o enterprise / site ops can set their users' security policies
> >     as that's part of their job and charter
> >
> > randy
> >
> I actually agree with you Chris and Steven. Point is though, that in a
> HUGE outbreak - sometimes you might even have to cause a self-DDoS and
> kill some of your services to parts of your networks or at all, to keep
> your net alive, not to mention secure.

This decision (to block port X or not in a large outbreak) is still a
network by network decision... Smaller or 'more tightly bound' networks
might have an easier time making that call, I'd bet that almost all of the
very large networks will look at each case and come to the same
1) our network isn't affected by this problem
2) our customers will be affected by a block
3) our customers should deal with security on their own, unless they are
paying for service which includes said blocking.

> As immediate critical measures, blocking tcp/445 might be an acceptable
> solution. Nobody is talking about censoring the Internet.

see above. and recall that there were several respondents to this thread
that were talking exactly about blocking tcp/445 to their customers, or on
their network, which is censoring.

The distinction Randy, and I and Steve, are making is that:
1) each network should decide on their own
2) each person deciding should understand the ramifications of that
3) each person deciding should keep in mind that they might not understand
all of their customers requirements for traffic.

> I believe that blocking port 445 is Good, just like I believe it will
> not get done by most and for Good reasons.

'good' 'in the right situation' which isn't 'across the network as a
whole'. Oh, do the current spate of tcp/445 problems also exist in the new
netbios of tcp/80 incarnations MS has cooked up? I'd venture to guess they
probably do... wanna block tcp/80 as well? :)

> Every solution has its good applications - sometimes short-term, even
> Bad long term solutions. Thing is, how do they remain temporary rather
> than becoming perm.?

This last sentence is a long and hard learned lesson :) Once you block
port X and people figure that out, they expect you to always block port X.
They drop their guard and focus on other problems, they have a new
'firewall' :( it's you.

>From the Slammer incident we learned that blocking 1434 for even a short
period of time made people complaicant. They didn't patch their broken
servers/systems until we unblocked the traffic and they got re-infected
again :(

Do not become the internet firewall for your large customer base... it's