155 lines
6.1 KiB
Text
155 lines
6.1 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-SA-16:02.ntp Security Advisory
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The FreeBSD Project
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Topic: ntp panic threshold bypass vulnerability
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Category: contrib
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Module: ntp
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Announced: 2016-01-14
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Credits: Network Time Foundation
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Affects: All supported versions of FreeBSD.
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Corrected: 2016-01-11 01:09:50 UTC (stable/10, 10.2-STABLE)
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2016-01-14 09:10:46 UTC (releng/10.2, 10.2-RELEASE-p9)
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2016-01-14 09:11:16 UTC (releng/10.1, 10.1-RELEASE-p26)
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2016-01-11 01:48:16 UTC (stable/9, 9.3-STABLE)
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2016-01-14 09:11:26 UTC (releng/9.3, 9.3-RELEASE-p33)
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CVE Name: CVE-2015-5300
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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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The ntpd(8) daemon is an implementation of the Network Time Protocol (NTP)
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used to synchronize the time of a computer system to a reference time
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source.
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II. Problem Description
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The ntpd(8) daemon has a safety feature to prevent excessive stepping of
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the clock called the "panic threshold". If ever ntpd(8) determines the
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system clock is incorrect by more than this threshold, the daemon exits.
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There is an implementation error within the ntpd(8) implementation of this
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feature, which allows the system time be adjusted in certain circumstances.
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III. Impact
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When ntpd(8) is started with the '-g' option specified, the system time will
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be corrected regardless of if the time offset exceeds the panic threshold (by
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default, 1000 seconds). The FreeBSD rc(8) subsystem allows specifying the
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'-g' option by either including '-g' in the ntpd_flags list or by enabling
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ntpd_sync_on_start in the system rc.conf(5) file.
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If at the moment ntpd(8) is restarted, an attacker can immediately respond to
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enough requests from enough sources trusted by the target, which is difficult
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and not common, there is a window of opportunity where the attacker can cause
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ntpd(8) to set the time to an arbitrary value.
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IV. Workaround
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No workaround is available, but systems not running ntpd(8), or running
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ntpd(8) but do not use ntpd_sync_on_start="YES" or specify the '-g' option in
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ntpd_flags are not affected. Neither of these are set by default.
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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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The ntpd service has to be restarted after the update. A reboot is
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recommended but not required.
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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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The ntpd service has to be restarted after the update. A reboot is
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recommended but not required.
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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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[FreeBSD 10.1 and 10.2]
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# fetch https://security.FreeBSD.org/patches/SA-16:02/ntp-10.patch
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# fetch https://security.FreeBSD.org/patches/SA-16:02/ntp-10.patch.asc
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# gpg --verify ntp-10.patch.asc
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[FreeBSD 9.3]
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# fetch https://security.FreeBSD.org/patches/SA-16:02/ntp-9.patch
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# fetch https://security.FreeBSD.org/patches/SA-16:02/ntp-9.patch.asc
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# gpg --verify ntp-9.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 the operating system using buildworld and installworld as
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described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.
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Restart the applicable daemons, or reboot the 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/9/ r293652
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releng/9.3/ r293896
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stable/10/ r293650
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releng/10.1/ r293894
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releng/10.2/ r293893
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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://www.cs.bu.edu/~goldbe/NTPattack.html>
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<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-5300>
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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-16:02.ntp.asc>
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