[Discuss] Port Scanning

[Dan Ritter]

Kent Borg wrote: 
> Anyway, finally to the point.
> 
> What is going on in this short excerpt (out of a very long e-mail of such
> stuff):
> 
> >     From 103.203.58.1 - 1 packet to tcp(8001)
> >     From 103.224.217.31 - 1 packet to tcp(23)
> >     From 103.229.127.36 - 1 packet to udp(1434)
> >     From 103.237.146.15 - 1 packet to udp(1900)
> >     From 103.252.89.123 - 12 packets to tcp(2995,15066,15825,17990,22787,50236,51764,52432,55508,61617)
> >     From 104.40.57.205 - 2 packets to tcp(110,2049)
> >     From 104.40.57.225 - 1 packet to tcp(26)
> >     From 104.40.74.178 - 1 packet to tcp(8888)
> 
> Most of it makes sense:

...
 
> But what about that those 12-packets 103.252.89.123 sent to 10 different
> high ports? (note 12 ≠ 10)
> 
> Are they really expecting services to be running up there? Are they trying
> to hit return port numbers through a broken NAT? Is that some default
> port-knocking pattern…? They are looking for 10-specific things but their
> script forget that they had already hit two of them? Or two of them are two
> different specific things and hitting those two ports for each case was just
> easier?

They are looking for specific vulnerabilities/existing malware.

> One day I scanned myself and I discovered it was listening on an unexpected
> port. Turns out I had Rhythmbox was running at the time, and it was
> helpfully defaulting to offering "DAAP Music Sharing". Probably not a big
> problem, but still something I don't want and I turned it off. A firewall
> prevents such accidental things from being accessible. But a firewall should
> not be a primary line of defense, dammit! And I should still occasionally
> scan local host, *and* turn off my firewall and scan my IP address(es) from
> a different machine…

The firewall is always a primary line of defense. It protects
your systems from things that you didn't intend to have running.
It also is a convenient method to deny access to specific
networks.

The secondary line of defense has to be identification,
authentication and authorization for each service that you *did*
mean to be running.

> P.P.S. My decades long dislike of firewalls is *finally* getting trendy with
> the impressive name "Zero Trust Architecture", it even has a TLA: "ZTA".

That's not what Zero Trust means.

Zero Trust means that you don't *grant* access based on the
sender's IP. (You can certainly deny access based on an IP.)
Every Zero Trust service needs to require an identity,
authenticate it, and only authorize the minimum necessary for
that identity in that context. That's it. And it's a terrible
name, but so many names are.


-dsr-

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