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FreeBSD-SA-15:27.bind Security Advisory
The FreeBSD Project

Topic: BIND remote denial of service vulnerability

Category: contrib
Module: bind
Announced: 2015-12-16
Credits: ISC
Affects: FreeBSD 9.x
Corrected: 2015-12-16 06:10:05 UTC (stable/9, 9.3-STABLE)
2015-12-16 06:21:26 UTC (releng/9.3, 9.3-RELEASE-p32)
CVE Name: CVE-2015-8000

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. The libdns
library is a library of DNS protocol support functions.

II. Problem Description

An error in the parsing of incoming responses allows some records with an
incorrect class to be be accepted by BIND instead of being rejected as
malformed. This can trigger a REQUIRE assertion failure when those records
are subsequently cached.

III. Impact

An attacker who can cause a server to request a record with a malformed class
attribute can use this bug to trigger a REQUIRE assertion in db.c, causing
named to exit and denying service to clients.

The risk to recursive servers is high. Authoritative servers are at limited
risk if they perform authentication when making recursive queries to resolve
addresses for servers listed in NS RRSETs.

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-15:27/bind.patch
# fetch https://security.FreeBSD.org/patches/SA-15:27/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 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/ r292320
releng/9.3/ r292321
– ————————————————————————-

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-01317>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-8000>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-15:27.bind.asc>
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