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============================================================================FreeBSD-SA-07:03.ipv6 Security Advisory
The FreeBSD Project
Topic: IPv6 Routing Header 0 is dangerous
Category: core
Module: ipv6
Announced: 2007-04-26
Credits: Philippe Biondi, Arnaud Ebalard, Jun-ichiro itojun Hagino
Affects: All FreeBSD releases.
Corrected: 2007-04-24 11:42:42 UTC (RELENG_6, 6.2-STABLE)
2007-04-26 23:42:23 UTC (RELENG_6_2, 6.2-RELEASE-p4)
2007-04-26 23:41:59 UTC (RELENG_6_1, 6.1-RELEASE-p16)
2007-04-24 11:44:23 UTC (RELENG_5, 5.5-STABLE)
2007-04-26 23:41:27 UTC (RELENG_5_5, 5.5-RELEASE-p12)
CVE Name: CVE-2007-2242
I. Background
IPv6 provides a routing header option which allows a packet sender to
indicate how the packet should be routed, overriding the routing knowledge
present in a network. This functionality is roughly equivalent to the
"source routing" option in IPv4. All nodes in an IPv6 network -- both
routers and hosts -- are required by RFC 2640 to process such headers.
II. Problem Description
There is no mechanism for preventing IPv6 routing headers from being used
to route packets over the same link(s) many times.
III. Impact
An attacker can "amplify" a denial of service attack against a link between
two vulnerable hosts; that is, by sending a small volume of traffic the
attacker can consume a much larger amount of bandwidth between the two
vulnerable hosts.
An attacker can use vulnerable hosts to "concentrate" a denial of service
attack against a victim host or network; that is, a set of packets sent
over a period of 30 seconds or more could be constructed such that they
all arrive at the victim within a period of 1 second or less.
Other attacks may also be possible.
IV. Workaround
No workaround is available.
V. Solution
NOTE WELL: The solution described below causes IPv6 type 0 routing headers
to be ignored. Support for IPv6 type 0 routing headers can be re-enabled
if required by setting the newly added net.inet6.ip6.rthdr0_allowed sysctl
to a non-zero value.
Perform one of the following:
1) Upgrade your vulnerable system to 5-STABLE, or 6-STABLE, or to the
RELENG_6_2, RELENG_6_1, or RELENG_5_5 security branch dated after the
correction date.
2) To patch your present system:
The following patches have been verified to apply to FreeBSD 5.5, 6.1,
and 6.2 systems.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch http://security.FreeBSD.org/patches/SA-07:03/ipv6.patch
# fetch http://security.FreeBSD.org/patches/SA-07:03/ipv6.patch.asc
b) Apply the patch.
# cd /usr/src
# patch < /path/to/patch
c) Recompile your kernel as described in