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FreeBSD-SA-16:24.ntp Security Advisory
The FreeBSD Project
Topic: Multiple vulnerabilities of ntp
Category: contrib
Module: ntp
Announced: 2016-06-04
Credits: Network Time Foundation and various contributors listed below
Affects: All supported versions of FreeBSD.
Corrected: 2016-06-03 08:59:21 UTC (stable/10, 10.3-STABLE)
2016-06-04 05:46:52 UTC (releng/10.3, 10.3-RELEASE-p5)
2016-06-04 05:46:52 UTC (releng/10.2, 10.2-RELEASE-p19)
2016-06-04 05:46:52 UTC (releng/10.1, 10.1-RELEASE-p36)
2016-06-03 09:03:10 UTC (stable/9, 9.3-STABLE)
2016-06-04 05:46:52 UTC (releng/9.3, 9.3-RELEASE-p44)
CVE Name: CVE-2016-4957, CVE-2016-4953, CVE-2016-4954, CVE-2016-4955
CVE-2016-4956
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit .
I. Background
The ntpd(8) daemon is an implementation of the Network Time Protocol (NTP)
used to synchronize the time of a computer system to a reference time
source.
II. Problem Description
Multiple vulnerabilities have been discovered in the NTP suite:
The fix for Sec 3007 in ntp-4.2.8p7 contained a bug that could cause ntpd to
crash. [CVE-2016-4957, Reported by Nicolas Edet of Cisco]
An attacker who knows the origin timestamp and can send a spoofed packet
containing a CRYPTO-NAK to an ephemeral peer target before any other
response is sent can demobilize that association. [CVE-2016-4953, Reported by
Miroslav Lichvar of Red Hat]
An attacker who is able to spoof packets with correct origin timestamps
from enough servers before the expected response packets arrive at the
target machine can affect some peer variables and, for example,
cause a false leap indication to be set. [CVE-2016-4954, Reported by
Jakub Prokes of Red Hat]
An attacker who is able to spoof a packet with a correct origin timestamp
before the expected response packet arrives at the target machine can
send a CRYPTO_NAK or a bad MAC and cause the association's peer variables
to be cleared. If this can be done often enough, it will prevent that
association from working. [CVE-2016-4955, Reported by Miroslav Lichvar
of Red Hat]
The fix for NtpBug2978 does not cover broadcast associations, so broadcast
clients can be triggered to flip into interleave mode. [CVE-2016-4956,
Reported by Miroslav Lichvar of Red Hat.]
III. Impact
Malicious remote attackers may be able to break time synchronization,
or cause the ntpd(8) daemon to crash.
IV. Workaround
No workaround is available, but systems not running ntpd(8) are not
affected. Network administrators are advised to implement BCP-38,
which helps to reduce the risk associated with the attacks.
V. Solution
Perform one of the following:
1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.
The ntpd service has to be restarted after the update. A reboot is
recommended but not required.
2) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:
# freebsd-update fetch
# freebsd-update install
The ntpd service has to be restarted after the update. A reboot is
recommended but not required.
3) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to the applicable
FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch https://security.FreeBSD.org/patches/SA-16:24/ntp.patch
# fetch https://security.FreeBSD.org/patches/SA-16:24/ntp.patch.asc
# gpg --verify ntp.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Recompile the operating system using buildworld and installworld as
described in .
Restart the applicable daemons, or reboot the system.
VI. Correction details
The following list contains the correction revision numbers for each
affected branch.
Branch/path Revision
- -------------------------------------------------------------------------
stable/9/ r301257
releng/9.3/ r301301
stable/10/ r301256
releng/10.1/ r301301
releng/10.2/ r301301
releng/10.3/ r301301
- -------------------------------------------------------------------------
To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:
# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
Or visit the following URL, replacing NNNNNN with the revision number:
VII. References
The latest revision of this advisory is available at
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