New Denial of Service Attack on Panix

Tue Sep 17 01:48:12 UTC 1996

Tim writes:
>> There are at least three things you can do to protect yourself from such
>> attacks. One is to patch your UNIX/BSD kernel to allow much higher numbers
>> of incomplete socket connections. One is to have another machine or your
>> network issue RST's for sockets that it thinks are part of the SYN flood
>> attack. And one is to install a SYN proxy machine between your net and the
>> Internet which catches all SYN packets and holds them until an ACK is
>> received at which point the SYN and the ACK are passed on to your network. 
>> Such a proxy can be built to handle HUGE numbers of incomplete conections.
>
>Great suggestion Mike!  Much quicker to do than a stochastic analysis
>of the pseudo-random nature of the attack (unless your the US goverment :-)
>and much cheaper to implement (unless your the US goverment :-)
>Certainly the UNIX proxy hack is easier than resorting to code-breaking,
>stochastic methods.
>Hats off to you,

I'm not sure it's even possible to analyze the pseudo-random shifting
attack (among other problems, there will be legitimate traffic in the
stream, so knowing what SYNs are bad is a pain) in anything approaching
realtime, so yes, one of the other methods is a much better choice 8-)

-george william herbert
gherbert at crl.com