Date: Mon, 25 Jun 2001 15:49:26 -0400 From: "alexus" <ml@db.nexgen.com> To: <freebsd-security@FreeBSD.ORG>, "Dag-Erling Smorgrav" <des@ofug.org> Subject: Re: disable traceroute to my host Message-ID: <016a01c0fdaf$f0aeb720$9865fea9@book> References: <20010622230217.JKT10107.mta05.onebox.com@onebox.com> <xzpr8w97w2g.fsf@flood.ping.uio.no>
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i'm thinkin to disable ttl=1 .. would that be ok with you? ----- Original Message ----- From: "Dag-Erling Smorgrav" <des@ofug.org> To: <freebsd-security@FreeBSD.ORG> Sent: Sunday, June 24, 2001 11:10 AM Subject: Re: disable traceroute to my host > "Kris Anderson" <ohshutup@zdnetmail.com> writes: > > You can put in a rule like > > > > ipfw add 3 deny icmp from any to FF.FF.FF.FF via F0 > > [...] > > AUUUUGH! > > First - the only one who got it right is Brooks Davis: no, it can't be > done. The best you can hope for is to prevent your own box (and > anything behind it, if it's a gateway) from responding to certain > specific types of traces, but the tracer will still be able to see > most of the route between you and him, and there are ways of tracing a > route that you can't block without also blocking a lot of legitimate > traffic. > > Second - traceroute is pretty harmless, and not really the corner- > stone of 3v1l h4ckd0m you people seem to think it is, so even if you > could prevent anyone from tracerouting you it wouldn't make much (or > even any) difference to an attacker's ability to harm you. > > Third - if you set up ipfw to unconditionally block ICMP (whether in > the mistaken belief that it will prevent route tracing or for some > other lameass reason), I will personally buy a very heavy baseball > bat, hop on a plane, and pay you a visit you'll remember for the rest > of your very short lives. Although some ICMP types are admittedly not > very useful, that doesn't mean none of them are, and you should at the > very least let types 3 and 11 through or you'll be very sorry. I > usually set up my filters to let 0, 3, 8 and 11 through and block > everything else. > > Fourth - this subject has been discussed to death on this very list > several times in the past. We keep searchable archives for a reason. > > Fifth - someone mentioned stealth routing. There's no such thing in > FreeBSD, but there's something called stealth forwarding, which I > wrote*, and which makes the TCP/IP stack neither decrement nor even > inspect the TTL on forwarded packets, so if someone traceroutes a host > behind you you won't show up in the trace, but if someone traceroutes > you it'll be business as usual. You need to add the IPSTEALTH option > to your kernel to enable support for this (and toggle a sysctl > variable to actually turn stealth forwarding on). > > DES > -- > Dag-Erling Smorgrav - des@ofug.org > > * It went a bit like this: Friend: "Sun have this new firewall product > that's really cool, it can do blah blah blah" - Me: "Oh, FreeBSD can > do that" - Friend: "No, it can't" - Me: "Yes, it can" - Friend: "No > it can't, because blah blah blah" - Me: "Oh, I see" <clicketyclick> > "Now FreeBSD can do that too" - Friend: <boggle> > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-security" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message
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