freebsd security - Jan 2014 - portscans and blackhole

Hello,

can someone please explain:

one of my boxes gets portscanned often by some likely infected laptops.
While having set

net.inet.tcp.blackhole=1

there are still messages like

+Limiting closed port RST response from 348 to 200 packets/sec

appearing. Are these RSTs actually sent out or does this just pop up
for some other reason ?

This is on 8.4-stable btw.

thanks,

Tee

Hello

On 20.01.14 12:31, sa9k063 wrote:
> can someone please explain:
>
> one of my boxes gets portscanned often by some likely infected laptops.
> While having set
>
> net.inet.tcp.blackhole=1
>
> there are still messages like
>
> +Limiting closed port RST response from 348 to 200 packets/sec
According to the blackhole(4) manpage (from a FreeBSD 9.1 system):

---8<------------------------------------------------------------
SYNOPSIS
      sysctl net.inet.tcp.blackhole[=[0 | 1 | 2]]
      sysctl net.inet.udp.blackhole[=[0 | 1]]

Part of DESCRIPTION:
Normal behaviour, when a TCP SYN segment is received on a port 
where there is no socket accepting connections, is for the system 
to return a RST segment, and drop the connection.  The connecting 
system will see this as a “Connection refused”.  By setting the 
TCP blackhole MIB to a numeric value of one, the incoming SYN 
segment is merely dropped, and no RST is sent, making the system 
appear as a blackhole.  By setting the MIB value to two, any 
segment arriving on a closed port is dropped without returning a 
RST.  This provides some degree of protection against stealth 
port scans.
---8<------------------------------------------------------------

So it is possible, that you are hit with something else then SYN 
packets and should probably set net.inet.tcp.blackhole=2, or even 
with UDP packets, then also set net.inet.udp.blackhole=1.

What output does 'sysctl -a | grep blackhole' show?


bye
Fabian
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