Date: Sun, 25 Feb 1996 11:48:33 -0700 From: Warner Losh <imp@village.org> To: "Garrett A. Wollman" <wollman@lcs.mit.edu> Cc: freebsd-security@FreeBSD.ORG Subject: Re: Alert: UDP Port Denial-of-Service Attack (fwd) Message-ID: <199602251848.LAA18341@rover.village.org> In-Reply-To: Your message of Sun, 25 Feb 1996 13:21:16 EST
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: However, it is trivial to get the daytime service to ping-pong with : the echo service. Same thing for the chargen service (don't know what : purpose that serves...) True, I'd forgotten that part. Chargen is for network testing. The original theory was to see if the UDP/TCP implementations are working. It is a good thing for that, but not good enough for this latest attack. : > UDP is, at present, the only thing impacted. It only takes one rogue : > packet to set them jabbering at each other (which is one reason we : > don't allow any IP packets with "src" of one of our netblock through : > our firewall). : : Of course, that doesn't help you if the forged source is on someone : else's network... That's why we also filter almost all inbound UDP messages as well :-) I think we let in DNS packets, and that is about it. : > I don't see how a TCP attack could succeed given the : > three way handshake that is required by TCP to establish a connection. : : Guess the Initial Sequence Number. On old BSD systems, this was : almost trivial. On modern BSD systems, this is much more difficult. I know that's how you make machine A think machine B is talking to it, but how do you do both sides such that connections will be established? The initial three way handshake is assymetric. Warnerhome | help
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