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Category:   Application (Generic)  >   ntp Vendors:   ntp.org
(FreeBSD Issues Fix) ntp Multiple Bugs Let Remote Users Modify Parameters and Deny Service
SecurityTracker Alert ID:  1036038
SecurityTracker URL:  http://securitytracker.com/id/1036038
CVE Reference:   CVE-2016-4953, CVE-2016-4954, CVE-2016-4955, CVE-2016-4956, CVE-2016-4957   (Links to External Site)
Date:  Jun 6 2016
Impact:   Denial of service via network, Modification of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): prior to 4.2.8p8
Description:   Multiple vulnerabilities were reported in ntp. A remote user can cause denial of service conditions on the target system. A remote user can modify configuration parameters in certain cases.

A remote user can send a specially crafted spoofed packet containing an invalid MAC to the target system to demobilize its ephemeral association [CVE-2016-4953].

A remote user can send specially crafted spoofed packets to bypass some validation checks in the receive() function and be processed by the process_packet() function in 'ntp_proto.c' [CVE-2016-4954]. In some cases, the remote user may be able to modify certain peer variables on the target system.

A remote user can send a specially crafted spoofed packet with an invalid MAC or crypto-NAK to the target system to reset its association and potentially prevent the association from working [CVE-2016-4955]. Systems using autokey for authentication are affected.

A remote user can send specially crafted data to cause a target broadcast client to switch to interleave mode and cause the client synchronization to become disabled [CVE-2016-4956].

A remote user can send a specially crafted crypto-NAK packet to the target system to trigger a null pointer dereference and cause the ntpd process to crash [CVE-2016-4957].

Jakub Prokes of Red Hat Quality Engineering, Miroslav Lichvar of Red Hat, and Nicolas Edet of Cisco reported these vulnerabilities.

Impact:   A remote user can modify configuration parameters in certain cases.

A remote user can cause denial of service conditions, including crashing the daemon, destabilizing ephemeral associations, and disabling synchronization.

Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

https://security.FreeBSD.org/advisories/FreeBSD-SA-16:24.ntp.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-16:24.ntp.asc (Links to External Site)
Cause:   Access control error, Input validation error, State error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  9.3, 10.1, 10.2, 10.3

Message History:   This archive entry is a follow-up to the message listed below.
Jun 6 2016 ntp Multiple Bugs Let Remote Users Modify Parameters and Deny Service



 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-16:24.ntp

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

=============================================================================
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 <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:

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 <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/                                                         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:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-4957>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-4953>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-4954>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-4955>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-4956>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:24.ntp.asc>
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