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FreeBSD-SA-18:02.ntp Security Advisory
The FreeBSD Project

Topic: Multiple vulnerabilities of ntp

Category: contrib
Module: ntp
Announced: 2018-03-07
Credits: Network Time Foundation
Affects: All supported versions of FreeBSD.
Corrected: 2018-02-28 09:01:03 UTC (stable/11, 11.1-STABLE)
2018-03-07 05:58:24 UTC (releng/11.1, 11.1-RELEASE-p7)
2018-03-01 04:06:49 UTC (stable/10, 10.4-STABLE)
2018-03-07 05:58:24 UTC (releng/10.4, 10.4-RELEASE-p6)
2018-03-07 05:58:24 UTC (releng/10.3, 10.3-RELEASE-p27)
CVE Name: CVE-2018-7182, CVE-2018-7170, CVE-2018-7184, CVE-2018-7185,
CVE-2018-7183

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

The ctl_getitem() function is used by ntpd(8) to process incoming “mode 6”
packets. A malicious “mode 6” packet can be sent to an ntpd instance, and
if the ntpd instance is from 4.2.8p6 through 4.2.8p10, ctl_getitem() will
read past the end of its buffer. [CVE-2018-7182]

The ntpd(8) service can be vulnerable to Sybil attacks. If a system is
configured 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-2018-7170]

The fix for NtpBug2952 was incomplete, and while it fixed one problem it
created another. Specifically, it drops bad packets before updating the
“received” timestamp. This means a third-party can inject a packet with
a zero-origin timestamp, meaning the sender wants to reset the association,
and the transmit timestamp in this bogus packet will be saved as the most
recent “received” timestamp. The real remote peer does not know this
value and this will disrupt the association until the association resets.
[CVE-2018-7184]

The NTP Protocol allows for both non-authenticated and authenticated
associations, in client/server, symmetric (peer), and several broadcast
modes. In addition to the basic NTP operational modes, symmetric mode and
broadcast servers can support an interleaved mode of operation. In
ntp-4.2.8p4, a bug was inadvertently introduced into the protocol engine that
allows a non-authenticated zero-origin (reset) packet to reset an
authenticated interleaved peer association. If an attacker can send a packet
with a zero-origin timestamp and the source IP address of the “other side” of
an interleaved association, the ‘victim’ ntpd will reset its association.
The attacker must continue sending these packets in order to maintain the
disruption of the association. [CVE-2018-7185]

The ntpq(8) utility is a monitoring and control program for ntpd. The
internal decodearr() function of ntpq(8) that is used to decode an array in
a response string when formatted data is being displayed. This is a problem
in affected versions of ntpq if a maliciously-altered ntpd returns an array
result that will trip this bug, or if a bad actor is able to read an ntpq(8)
request on its way to a remote ntpd server and forge and send a response
before the remote ntpd sends its response. It is potentially possible that
the malicious data could become injectable/executable code. [CVE-2017-7183]

III. Impact

Malicious remote attackers may be able to break time synchornization,
or cause the ntpq(8) utility to crash.

IV. Workaround

No workaround is available, but systems not running ntpd(8) or ntpq(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.

[FreeBSD 11.1]
# fetch https://security.FreeBSD.org/patches/SA-18:02/ntp-11.1.patch
# fetch https://security.FreeBSD.org/patches/SA-18:02/ntp-11.1.patch.asc
# gpg –verify ntp-11.1.patch.asc

[FreeBSD 10.4]
# fetch https://security.FreeBSD.org/patches/SA-18:02/ntp-10.4.patch
# fetch https://security.FreeBSD.org/patches/SA-18:02/ntp-10.4.patch.asc
# gpg –verify ntp-10.4.patch.asc

[FreeBSD 10.3]
# fetch https://security.FreeBSD.org/patches/SA-18:02/ntp-10.3.patch
# fetch https://security.FreeBSD.org/patches/SA-18:02/ntp-10.3.patch.asc
# gpg –verify ntp-10.3.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/10/ r330141
releng/10.3/ r330567
releng/10.4/ r330567
stable/11/ r330106
releng/11.1/ r330567
– ————————————————————————-

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#February_2018_ntp_4_2_8p11_NTP_S>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7182>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7170>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7184>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7185>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7183>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:02.ntp.asc>
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