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Posted on 29 April 2016
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FreeBSD-SA-16:16.ntp Security Advisory
The FreeBSD Project
Topic: Multiple vulnerabilities of ntp
Category: contrib
Module: ntp
Announced: 2016-04-29
Credits: Network Time Foundation and various contributors listed below
Affects: All supported versions of FreeBSD.
Corrected: 2016-04-27 15:24:33 UTC (stable/10, 10.3-STABLE)
2016-04-29 08:02:31 UTC (releng/10.3, 10.3-RELEASE-p1)
2016-04-29 08:02:31 UTC (releng/10.2, 10.2-RELEASE-p15)
2016-04-29 08:02:31 UTC (releng/10.1, 10.1-RELEASE-p32)
2016-04-27 15:25:18 UTC (stable/9, 9.3-STABLE)
2016-04-29 08:02:31 UTC (releng/9.3, 9.3-RELEASE-p40)
CVE Name: CVE-2016-1547, CVE-2016-1548, CVE-2016-1549, CVE-2016-1550,
CVE-2016-1551, CVE-2016-2516, CVE-2016-2517, CVE-2016-2518,
CVE-2016-2519
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.
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:
On OSes (FreeBSD not affected) that allows packets claiming to be from
127.0.0.0/8 that arrive over physical network, if ntpd is configured to use
a reference clock, an attacker can inject packets over the network that look
like they are coming from that reference clock. [CVE-2016-1551, Reported by
Matt Street and others of Cisco ASIG]
If a system is set up to use a trustedkey, and if one is not using the
feature introduced in ntp-4.2.8p6 allowing an optional 4th field in the
ntp.keys file to specify which IPs can serve time, a malicious
authenticated peer -- i.e. one where the attacker knows the private
symmetric key -- can create arbitrarily-many ephemeral associations in
order to win the clock selection of ntpd and modify a victim's clock.
[CVE-2016-1549, Reported by Matthew Van Gundy of Cisco ASIG]
If ntpd was expressly configured to allow for remote configuration (this is
not common), a malicious user who knows the controlkey for ntpq or the
requestkey for ntpdc (if mode7 is expressly enabled) can create a session
with ntpd and if an existing association is unconfigured using the same IP
twice on the unconfig directive line, ntpd will abort. [CVE-2016-2516,
Reported by Yihan Lian of the Cloud Security Team, Qihoo 360]
If ntpd was expressly configured to allow for remote configuration (this is
not common), a malicious user who knows the controlkey for ntpq or the
requestkey for ntpdc (if mode7 is expressly enabled) can create a session
with ntpd and then send a crafted packet to ntpd that will change the value
of the trustedkey, controlkey, or requestkey to a value that will prevent
any subsequent authentication with ntpd until ntpd is restarted.
[CVE-2016-2517, Reported by Yihan Lian of the Cloud Security Team, Qihoo 360]
Using a crafted packet to create a peer association with hmode > 7 causes
the MATCH_ASSOC() lookup to make an out-of-bounds reference. [CVE-2016-2518,
Reported by Yihan Lian of the Cloud Security Team, Qihoo 360]
ntpq and ntpdc can be used to store and retrieve information in ntpd. It is
possible to store a data value that is larger than the size of the buffer
that the ctl_getitem() function of ntpd uses to report the return value.
If the length of the requested data value returned by ctl_getitem() is too
large, the value NULL is returned instead. There are 2 cases where the return
value from ctl_getitem() was not directly checked to make sure it's not NULL,
but there are subsequent INSIST() checks that make sure the return value is
not NULL. There are no data values ordinarily stored in ntpd that would
exceed this buffer length. But if one has permission to store values and
one stores a value that is "too large", then ntpd will abort if an attempt
is made to read that oversized value. [CVE-2016-2519, Reported by
Yihan Lian of the Cloud Security Team, Qihoo 360]
For ntp-4 versions up to but not including ntp-4.2.8p7, an off-path attacker
can cause a preemptable client association to be demobilized by sending a
crypto NAK packet to a victim client with a spoofed source address of an
existing associated peer. This is true even if authentication is enabled.
Furthermore, if the attacker keeps sending crypto NAK packets, for example
one every second, the victim never has a chance to reestablish the
association and synchronize time with that legitimate server. For ntp-4.2.8
up to ntp-4.2.8p6 there is less risk because more stringent checks are
performed on incoming packets, but there are still ways to exploit this
vulnerability in versions before ntp-4.2.8p7. [CVE-2016-1547, Reported by
Stephen Gray and Matthew Van Gundy of Cisco ASIG]
It is possible to change the time of an ntpd client or deny service to an
ntpd client by forcing it to change from basic client/server mode to
interleaved symmetric mode. An attacker can spoof a packet from a legitimate
ntpd server with an origin timestamp that matches the peer->dst timestamp
recorded for that server. After making this switch, the client will reject
all future legitimate server responses. It is possible to force the victim
client to move time after the mode has been changed. ntpq gives no
indication that the mode has been switched. [CVE-2016-1548, Reported by
Miroslav Lichvar of RedHat and separately by Jonathan Gardner of
Cisco ASIG]
Packet authentication tests have been performed using memcmp() or possibly
bcmp(), and it is potentially possible for a local or perhaps LAN-based
attacker to send a packet with an authentication payload and indirectly
observe how much of the digest has matched. [CVE-2016-1550, Reported
independently by Loganaden Velvindron, and Matthew Van Gundy and
Stephen Gray of Cisco ASIG]
III. Impact
Malicious remote attackers may be able to break time synchornization,
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 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-16:16/ntp.patch
# fetch https://security.FreeBSD.org/patches/SA-16:16/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 <URL:https://www.FreeBSD.org/handbook/makeworld.html>.
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/ r298700
releng/9.3/ r298770
stable/10/ r298699
releng/10.1/ r298770
releng/10.2/ r298770
releng/10.3/ r298770
- -------------------------------------------------------------------------
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:
<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
VII. References
<URL:http://support.ntp.org/bin/view/Main/SecurityNotice#April_2016_NTP_4_2_8p7_Security>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1547>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1548>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1549>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1550>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1551>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2516>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2517>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2518>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2519>
The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:16.ntp.asc>
