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FreeBSD-SA-16:28.bind                                       Security Advisory
                                                          The FreeBSD Project

Topic:          BIND remote Denial of Service vulnerability

Category:       contrib
Module:         bind
Announced:      2016-10-10
Credits:        ISC
Affects:        FreeBSD 9.x
Corrected:      2016-09-28 06:11:01 UTC (stable/9, 9.3-STABLE)
                2016-10-10 07:19:16 UTC (releng/9.3, 9.3-RELEASE-p48)
CVE Name:       CVE-2016-2776

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

BIND 9 is an implementation of the Domain Name System (DNS) protocols.
The named(8) daemon is an Internet Domain Name Server.

II.  Problem Description

Testing by ISC has uncovered a critical error condition which can occur when
a nameserver is constructing a response.  A defect in the rendering of
messages into packets can cause named to exit with an assertion failure in
buffer.c while constructing a response to a query that meets certain
criteria.

This assertion can be triggered even if the apparent source address is not
allowed to make queries (i.e. doesn't match 'allow-query'). [CVE-2016-2776]

III. Impact

A remote attacker who can send queries to a server running BIND can cause
the server to crash, resulting in a Denial of Service condition.

IV.  Workaround

No workaround is available, but hosts not running named(8) are not
vulnerable.

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 named 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 named 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 9.3]
# fetch https://security.FreeBSD.org/patches/SA-16:28/bind.patch
# fetch https://security.FreeBSD.org/patches/SA-16:28/bind.patch.asc
# gpg --verify bind.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 named service, or reboot the system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/9/                                                         r306394
releng/9.3/                                                       r306942
- -------------------------------------------------------------------------

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://kb.isc.org/article/AA-01419>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-2776>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:28.bind.asc>
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