153 lines
5.9 KiB
Text
153 lines
5.9 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-SA-15:09.ipv6 Security Advisory
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The FreeBSD Project
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Topic: Denial of Service with IPv6 Router Advertisements
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Category: core
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Module: ipv6
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Announced: 2015-04-07
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Credits: Dennis Ljungmark
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Affects: All supported versions of FreeBSD.
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Corrected: 2015-04-07 20:20:24 UTC (stable/10, 10.1-STABLE)
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2015-04-07 20:21:01 UTC (releng/10.1, 10.1-RELEASE-p9)
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2015-04-07 20:20:44 UTC (stable/9, 9.3-STABLE)
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2015-04-07 20:21:23 UTC (releng/9.3, 9.3-RELEASE-p13)
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2015-04-07 20:20:44 UTC (stable/8, 8.4-STABLE)
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2015-04-07 20:21:23 UTC (releng/8.4, 8.4-RELEASE-p27)
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CVE Name: CVE-2015-2923
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For general information regarding FreeBSD Security Advisories,
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including descriptions of the fields above, security branches, and the
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following sections, please visit <URL:https://security.FreeBSD.org/>.
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I. Background
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IPv6 nodes use the Neighbor Discovery protocol to determine the link-layer
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address of other nodes, find routers, and maintain reachability information.
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Routers advertise their presence together with various link and Internet
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parameters either periodically, or in response to a Router Solicitation
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message, using Router Advertisement (ICMPv6 type 134).
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II. Problem Description
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The Neighbor Discover Protocol allows a local router to advertise a
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suggested Current Hop Limit value of a link, which will replace
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Current Hop Limit on an interface connected to the link on the FreeBSD
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system.
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III. Impact
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When the Current Hop Limit (similar to IPv4's TTL) is small, IPv6 packets
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may get dropped before they reached their destinations.
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By sending specifically crafted Router Advertisement packets, an attacker
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on the local network can cause the FreeBSD system to lose the ability to
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communicate with another IPv6 node on a different network.
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IV. Workaround
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Only systems that are manually configured to use "accept_rtadv"
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ifconfig(8) flag on an interface are affected.
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The system administrator may decide to disable acceptance of Router
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Advertisements from untrusted network in a per-interface basis, by
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removing accept_rtadv flag at run time using ifconfig(8):
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ifconfig em0 inet6 -accept_rtadv
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Note that an interface does not accept Router Advertisement messages
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by default even if an IPv6 address is configured. One can know
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whether an interface is accepting Router Advertisement message or not
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from existence of ACCEPT_RTADV in "nd6 options" line in an output of
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ifconfig(8):
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nd6 options=23<PERFORMNUD,ACCEPT_RTADV,AUTO_LINKLOCAL>
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V. Solution
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Perform one of the following:
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1) Upgrade your vulnerable system to a supported FreeBSD stable or
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release / security branch (releng) dated after the correction date.
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2) To update your vulnerable system via a binary patch:
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Systems running a RELEASE version of FreeBSD on the i386 or amd64
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platforms can be updated via the freebsd-update(8) utility:
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# freebsd-update fetch
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# freebsd-update install
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3) To update your vulnerable system via a source code patch:
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The following patches have been verified to apply to the applicable
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FreeBSD release branches.
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a) Download the relevant patch from the location below, and verify the
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detached PGP signature using your PGP utility.
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# fetch https://security.FreeBSD.org/patches/SA-15:09/ipv6.patch
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# fetch https://security.FreeBSD.org/patches/SA-15:09/ipv6.patch.asc
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# gpg --verify ipv6.patch.asc
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b) Apply the patch. Execute the following commands as root:
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# cd /usr/src
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# patch < /path/to/patch
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c) Recompile your kernel as described in
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<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
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system.
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VI. Correction details
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The following list contains the correction revision numbers for each
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affected branch.
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Branch/path Revision
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- -------------------------------------------------------------------------
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stable/8/ r281231
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releng/8.4/ r281233
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stable/9/ r281231
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releng/9.3/ r281233
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stable/10/ r281230
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releng/10.1/ r281232
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- -------------------------------------------------------------------------
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To see which files were modified by a particular revision, run the
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following command, replacing NNNNNN with the revision number, on a
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machine with Subversion installed:
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# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
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Or visit the following URL, replacing NNNNNN with the revision number:
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<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
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VII. References
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<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-2923>
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The latest revision of this advisory is available at
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<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-15:09.ipv6.asc>
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