TCP RST attack

[Jacques A. Vidrine]

On Tue, Apr 20, 2004 at 07:44:37PM +0200, Dag-Erling Smørgrav wrote:
> Mike Tancsa <mike at sentex.net> writes:
> > http://www.uniras.gov.uk/vuls/2004/236929/index.htm
> 
> The advisory grossly exaggerates the impact and severity of this
> fea^H^H^Hbug.  The attack is only practical if you already know the
> details of the TCP connection you are trying to attack, or are in a
> position to sniff it.  

Well, the whole point is that *although in the past it was widely
believed otherwise*, this attack is practical today in some real world
situations.  It many cases the only unknown is the source port number,
and even that can be predictable.

[...]
> I don't believe BGP sessions are as exposed as the advisory claims
> they are, either.  The possibility of insertion attacks (which are
> quite hard) was predicted six years ago, when RFC 2385 (Protection of
> BGP Sessions via the TCP MD5 Signature Option) was written.  RST
> attacks may cause route flapping, but that can be avoided with a short
> hysteresis (though this may be impractical for backbone routers)

If the DoS attack causes route flapping, then the attack is a success.

> Insertion attacks against SSL connections are practically impossible,
> so the only risk there is an RST attack, which most browsers should
> handle gracefully.
> 
> DNS connections (even zone transfers) are so short-lived that you
> would have to be very, very lucky to pull off an insertion or RST
> attack against.

Yes, these seem to be stretches.

> The most likely attack scenario to come out of this is probably gamers
> and IRC weenies kicking eachother off servers (the server's IP address
> and port number are known, the servers often reveal client IP
> addresses to other clients, and the client often uses a fixed source
> port, or one from a relatively small range)

Every time someone is kicked off an IRC server (or otherwise restrained
from online chat), global productivity rises :-)

Cheers,
-- 
Jacques Vidrine / nectar at celabo.org / jvidrine at verio.net / nectar at freebsd.org