Re: syn flood attacks from NL-based netblocks

[Matt Harris <matt () netfire net>]

On Fri, Aug 16, 2019 at 5:05 PM Jim Shankland <nanog () shankland org> wrote:

> 1. Rate seems too slow to do any actual damage (is anybody really
> bothered by a few bad SYN packets per second per service, at this
> point?); but

Common technique used by port scanners to evade detection as a DoS attack
by fw/ids/etc.

2. IPs/port combinations with actual open services are being targeted
> (I'm seeing ports 22, 443, and 53, just at a glance, to specific IPs
> with those services running), implying somebody checked for open
> services first;

Or they're just checking if certain common ports are open with the
intention of later trying known exploits against those which are reachable
in order to attempt to compromise the hosts. Build the DB of reachable
hosts/ports now, come back with exploits later.

3. I'm seeing this in at least 2 locations, to addresses in different,
> completely unrelated ASes, implying it may be pretty widespread.

Sounds like a relatively common pattern though.

Is anybody else seeing the same thing? Any thoughts on what's going on?
> Or should I just be ignoring this and getting on with the weekend?

I wouldn't worry too much about it unless you have reason to believe some
of the likely-forthcoming exploits may actually work. Of course, if that's
the case, you should fix them anyhow.

Have a good weekend!