Another IPv6 related FreeBSD security advisory. freebsd-update fetch;freebsd-update install then reboot to apply new kernel. (-p5 or newer) Given the description, I believe that an ipfw rule of: deny log ip6 from any to any not antispoof in via tun0 would appropriately allow link-local on any non-tunnel interface, but prevent inappropriate data from coming spoofed in from the tunnel. It is important to specify an interface, as "antispoof" in ipfw will block link-local even if the interface has a link-local address (bug or not, that is how it works today) Your mileage may vary in the future. -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 ============================================================================= FreeBSD-SA-08:10.nd6 Security Advisory The FreeBSD Project Topic: IPv6 Neighbor Discovery Protocol routing vulnerability Category: core Module: sys_netinet6 Announced: 2008-10-01 Credits: David Miles Affects: All supported versions of FreeBSD. Corrected: 2008-10-01 00:32:59 UTC (RELENG_7, 7.1-PRERELEASE) 2008-10-01 00:32:59 UTC (RELENG_7_0, 7.0-RELEASE-p5) 2008-10-01 00:32:59 UTC (RELENG_6, 6.4-PRERELEASE) 2008-10-01 00:32:59 UTC (RELENG_6_3, 6.3-RELEASE-p5) CVE Name: CVE-2008-2476 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:http://security.FreeBSD.org/>. I. Background IPv6 nodes use the Neighbor Discovery protocol to determine the link-layer address of other nodes, find routers, and maintain reachability information. The Neighbor Discovery protocol uses Neighbor Solicitation (ICMPv6 type 135) to query target nodes for their link-layer addresses. II. Problem Description IPv6 routers may allow "on-link" IPv6 nodes to create and update the router's neighbor cache and forwarding information. A malicious IPv6 node sharing a common router but on a different physical segment from another node may be able to spoof Neighbor Discovery messages, allowing it to update router information for the victim node. III. Impact An attacker on a different physical network connected to the same IPv6 router as another node could redirect IPv6 traffic intended for that node. This could lead to denial of service or improper access to private network traffic. IV. Workaround Firewall packet filters can be used to filter incoming Neighbor Solicitation messages but may interfere with normal IPv6 operation if not configured carefully. Reverse path forwarding checks could be used to make gateways, such as routers or firewalls, drop Neighbor Solicitation messages from nodes with unexpected source addresses on a particular interface. IPv6 router administrators are encouraged to read RFC 3756 for further discussion of Neighbor Discovery security implications. V. Solution NOTE WELL: The solution described below causes IPv6 Neighbor Discovery Neighbor Solicitation messages from non-neighbors to be ignored. This can be re-enabled if required by setting the newly added net.inet6.icmp6.nd6_onlink_ns_rfc4861 sysctl to a non-zero value. Perform one of the following: 1) Upgrade your vulnerable system to 6-STABLE, or 7-STABLE, or to the RELENG_7_0, or RELENG_6_3 security branch dated after the correction date. 2) To patch your present system: The following patches have been verified to apply to FreeBSD 6.3 and 7.0 systems. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. [FreeBSD 6.3] # fetch http://security.FreeBSD.org/patches/SA-08:10/nd6-6.patch # fetch http://security.FreeBSD.org/patches/SA-08:10/nd6-6.patch.asc [FreeBSD 7.0] # fetch http://security.FreeBSD.org/patches/SA-08:10/nd6-7.patch # fetch http://security.FreeBSD.org/patches/SA-08:10/nd6-7.patch.asc b) Apply the patch. # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in <URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the system. VI. Correction details The following list contains the revision numbers of each file that was corrected in FreeBSD. Branch Revision Path - ------------------------------------------------------------------------- RELENG_6 src/sys/netinet6/in6.h 1.36.2.10 src/sys/netinet6/in6_proto.c 1.32.2.10 src/sys/netinet6/nd6.h 1.19.2.4 src/sys/netinet6/nd6_nbr.c 1.29.2.11 RELENG_6_3 src/UPDATING 1.416.2.37.2.10 src/sys/conf/newvers.sh 1.69.2.15.2.9 src/sys/netinet6/in6.h 1.36.2.8.2.1 src/sys/netinet6/in6_proto.c 1.32.2.8.2.1 src/sys/netinet6/nd6.h 1.19.2.2.6.1 src/sys/netinet6/nd6_nbr.c 1.29.2.9.2.1 RELENG_7 src/sys/netinet6/in6.h 1.51.2.2 src/sys/netinet6/in6_proto.c 1.46.2.3 src/sys/netinet6/nd6.h 1.21.2.2 src/sys/netinet6/nd6_nbr.c 1.47.2.3 RELENG_7_0 src/UPDATING 1.507.2.3.2.9 src/sys/conf/newvers.sh 1.72.2.5.2.9 src/sys/netinet6/in6.h 1.51.4.1 src/sys/netinet6/in6_proto.c 1.46.4.1 src/sys/netinet6/nd6.h 1.21.4.1 src/sys/netinet6/nd6_nbr.c 1.47.4.1 - ------------------------------------------------------------------------- VII. References http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-2476 http://www.kb.cert.org/vuls/id/472363 The latest revision of this advisory is available at http://security.FreeBSD.org/advisories/FreeBSD-SA-08:10.nd6.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkjkF2cACgkQFdaIBMps37KWWgCZAfug94zPIdkzW0tdIdSDzH/0 j18AnjypvJrRtzeQqhJkRU9wQWozgWvj =ieTi -----END PGP SIGNATURE-----