Date: Fri, 01 Jun 2012 13:12:41 -0600 From: Kurt Seifried <kseifried@...hat.com> To: oss-security@...ts.openwall.com CC: John Haxby <john.haxby@...cle.com> Subject: Re: CVE Request -- kernel: tcp: drop SYN+FIN messages -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 06/01/2012 10:35 AM, John Haxby wrote: > I am inclined to think that we should have a separate CVE for the > kernel here. Unless I'm mistaken, a packet with SYN+FIN has no > legitimate business being in the Internet any more than the old > SYN+RST has. It's security hardening in that firewall rules to > discard packets with odd combinations of flags are often deployed > by people setting up "serious" firewalls but most machines out > there, whether or not they have iptables set up, don't go to those > lengths. Certainly none of the machines I have access to that have > "out of the box" iptables configurations would appear to defend > against SYN+FIN for open ports. In my limited testing with iptables on RHEL 6.2 it appears that - --state NEW works properly, and won't allow SYN+FIN to create connections (I used hping3 and the SYN+FIN Packets were blocked). So the default ruleset: - -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT - -A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j DROP - -A INPUT -j REJECT --reject-with icmp-host-prohibited should work, so you could do you clever --syn bits first and then have that set to protect stuff from SYN+FIN. - -- Kurt Seifried Red Hat Security Response Team (SRT) PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQIcBAEBAgAGBQJPyRQpAAoJEBYNRVNeJnmTTxEQAJedLa1Xc6R3nVawEyxp3OLo 5+HTXnjW6SDLELpkV3abUUeZswrY7F3IYN6hKrcLm+1lCsTmubP5fhGa8Ta1RceH GqyxCn+7OTFr3JfT8nHIhV9bSNCIPpPStaVO319WfVNVOqvzXnmVeTid0AuMLOem DIgwLpZx/WQqxTXY26t3nabrnolVIZdlV7zMxyV+k8OC7kzyU80cCbG4n6ErDcpj rPcydQVa6GTxidX+CzEXtsnVUWfHBcVwQLO60biHOjD7S0ZCHbQhMrj/CA9RAPsH 9ltWC5sw6VSSGWv2J07dzop4IPzIUJeX/fMzI3HLGvhFuUPbH6AjgiadE0mgBlmB A3sXJAGr4yZqkUD/Z09tfy20RR+UFfao9dlR4MdBvigPVfPXJIgYAwP0R8s7wDA5 SPiQ52mYV+PwgH1akEZjtq4aj25RbSXWwqn/ALVu1Dqau77ti6+MVLu9+uxCx0S8 ZURyt0/OJjQXF6qrEtYZeaAz8OpaOTp8qaPAngoY9gtBFiHQW9xUDFpUMhvabGMO gmV3E5+DZ/+PQu1RbVfb4Ou65/yhS1daophXeiGCGeysW3rEoqvw/kESfeDMkotL WoxRGT4Jhg4JnqykuF5Z5A/U+EeqSI9qVgmkjkq30YU4MZb+teEmuitTTjWHu3LU V/y1Emz8j7zDb7Xi2I2h =e4JD -----END PGP SIGNATURE-----
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