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FreeBSD-SA-10:02.ntpd                                       Security Advisory
                                                          The FreeBSD Project

Topic:          ntpd mode 7 denial of service

Category:       contrib
Module:         ntpd
Announced:      2010-01-06
Affects:        All supported versions of FreeBSD.
Corrected:      2010-01-06 21:45:30 UTC (RELENG_8, 8.0-STABLE)
                2010-01-06 21:45:30 UTC (RELENG_8_0, 8.0-RELEASE-p2)
                2010-01-06 21:45:30 UTC (RELENG_7, 7.2-STABLE)
                2010-01-06 21:45:30 UTC (RELENG_7_2, 7.2-RELEASE-p6)
                2010-01-06 21:45:30 UTC (RELENG_7_1, 7.1-RELEASE-p10)
                2010-01-06 21:45:30 UTC (RELENG_6, 6.4-STABLE)
                2010-01-06 21:45:30 UTC (RELENG_6_4, 6.4-RELEASE-p9)
                2010-01-06 21:45:30 UTC (RELENG_6_3, 6.3-RELEASE-p15)
CVE Name:       CVE-2009-3563

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://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

If ntpd receives a mode 7 (MODE_PRIVATE) request or error response
from a source address not listed in either a 'restrict ... noquery'
or a 'restrict ... ignore' section it will log the even and send
a mode 7 error response.

III. Impact

If an attacker can spoof such a packet from a source IP of an affected
ntpd to the same or a different affected ntpd, the host(s) will endlessly
send error responses to each other and log each event, consuming network
bandwidth, CPU and possibly disk space.

IV.  Workaround

Proper filtering of mode 7 NTP packets by a firewall can limit the
number of systems used to attack your resources.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 6-STABLE, 7-STABLE or 8-STABLE,
or to the RELENG_8_0, RELENG_7_2, RELENG_7_1, RELENG_6_4, or
RELENG_6_3 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 6.3, 6.4,
7.1, 7.2, and 8.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-10:02/ntpd.patch
# fetch http://security.FreeBSD.org/patches/SA-10:02/ntpd.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/usr.sbin/ntp/ntpd
# make obj && make depend && make && make install
# /etc/rc.d/ntpd restart

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_6
  src/contrib/ntp/ntpd/ntp_request.c                          1.1.1.4.8.2
RELENG_6_4
  src/UPDATING                                            1.416.2.40.2.13
  src/sys/conf/newvers.sh                                  1.69.2.18.2.15
  src/contrib/ntp/ntpd/ntp_request.c                      1.1.1.4.8.1.2.1
RELENG_6_3
  src/UPDATING                                            1.416.2.37.2.20
  src/sys/conf/newvers.sh                                  1.69.2.15.2.19
  src/contrib/ntp/ntpd/ntp_request.c                         1.1.1.4.20.1
RELENG_7
  src/contrib/ntp/ntpd/ntp_request.c                         1.1.1.4.18.2
RELENG_7_2
  src/UPDATING                                             1.507.2.23.2.9
  src/sys/conf/newvers.sh                                  1.72.2.11.2.10
  src/contrib/ntp/ntpd/ntp_request.c                     1.1.1.4.18.1.4.1
RELENG_7_1
  src/UPDATING                                            1.507.2.13.2.13
  src/sys/conf/newvers.sh                                   1.72.2.9.2.14
  src/contrib/ntp/ntpd/ntp_request.c                     1.1.1.4.18.1.2.1
RELENG_8
  src/contrib/ntp/ntpd/ntp_request.c                              1.2.2.1
RELENG_8_0
  src/UPDATING                                              1.632.2.7.2.5
  src/sys/conf/newvers.sh                                    1.83.2.6.2.5
  src/contrib/ntp/ntpd/ntp_request.c                              1.2.4.1
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/6/                                                         r201679
releng/6.4/                                                       r201679
releng/6.3/                                                       r201679
stable/7/                                                         r201679
releng/7.2/                                                       r201679
releng/7.1/                                                       r201679
stable/8/                                                         r201679
releng/8.0/                                                       r201679
head/                                                             r200576
- -------------------------------------------------------------------------

VII. References

http://support.ntp.org/bin/view/Main/SecurityNotice#DoS_attack_from_certain_NTP_mode
https://support.ntp.org/bugs/show_bug.cgi?id=1331
http://www.kb.cert.org/vuls/id/568372
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-3563

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-10:02.ntpd.asc
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