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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
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