Re: DoS against DHCP

[Russell Handorf <rhandorf () mail russells-world com>]

#!/bin/sh
counter=0
if [ $# -eq 0 ]
then
        echo "You're missing the arguement of how many times for me to 
repeat."
        exit 1
fi
while [ $counter -le $1 ]
do
        ifconfig eth0 down
        ./changemac -r
        pump
        ifconfig eth0
        coutner=`expr $counter + 1`
done
echo "done"

Contingent on you having changemac or some other way to randomize a new mac 
addy.

russ

At 02:20 PM 1/30/2002 -0800, you wrote:

>         I came up with this about a year back at DefCon, and told some 
> friends
> in hopes that either they or I would do something with it, but none of us had
> time so here goes, and please feel free to write this yourself.  DoS against
> DHCP:
>
>         A DHCP server has only a certain amount of addresses availible.  If
> you (a single malicious machine connected to the network) actively take up all
> availible IP address, and compete against the machines that are currently
> connected you should be able to completely take all availible IP addresses and
> block access to the DHCP server.  You could do this by opening many interfaces
> on a linux box and asking for many DHCP addresses and lying that you connected
> before any competing machines (or DoS the competing machine directly until the
> DHCP server releases the IP address to you).
>
>         This combined with war-driving could take down any DHCP IP address
> block within wireless range.  Kinda nasty, but only effective as long as you
> stay connected to the network, so a compromised machine on the network 
> might be
> necessary for extended DoS.  Probably the way around this would be a) some 
> sort
> of authentication to log into the DHCP server and or b) using leap or 
> something
> similar.  MAC addresses are spoofable, so it probably wouldn't be a good idea
> to limit the number of times a particular MAC address connects to the network,
> as that would just be a sloppy obfuscation.  DHCP has always seemed like a bad
> idea to me.  Sorry if this seems obvious.

==================================
Russell Handorf
oooo, shiney ::Wanders after it::

www.russells-world.com
www.philly2600.net

"Computer games don't affect kids, I mean if Pacman affected us as kids, 
we'd all be running around in darkened rooms, munching pills and listening 
to repetitive music." ~unknown
==================================