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Category:   Application (Generic)  >   BIND Vendors:   ISC (Internet Software Consortium)
(FreeBSD Issues Fix) BIND RRSIG RRsets Negative Caching Off-by-one Bug Lets Remote Users Deny Service
SecurityTracker Alert ID:  1025575
SecurityTracker URL:
CVE Reference:   CVE-2011-1910   (Links to External Site)
Date:  May 28 2011
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): 9.4-ESV-R3 and later, 9.6-ESV-R2 and later, 9.6.3, 9.7.1 and later, 9.8.0 and later; prior to 9.4-ESV-R4-P1, 9.6-ESV-R4-P1, 9.7.3-P1, 9.8.0-P2
Description:   A vulnerability was reported in BIND. A remote user can cause denial of service conditions.

A remote DNS server can supply very large RRSIG RRsets in a negative response to trigger an off-by-one error in a buffer size check and cause the target requesting named process to crash.

Impact:   A remote user can cause named to crash.
Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Access control error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  7.3, 7.4, 8.1, and 8.2

Message History:   This archive entry is a follow-up to the message listed below.
May 27 2011 BIND RRSIG RRsets Negative Caching Off-by-one Bug Lets Remote Users Deny Service

 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-11:02.bind

Hash: SHA1

FreeBSD-SA-11:02.bind                                       Security Advisory
                                                          The FreeBSD Project

Topic:          BIND remote DoS with large RRSIG RRsets and negative caching

Category:       contrib
Module:         bind
Announced:      2011-05-28
Credits:        Frank Kloeker, Michael Sinatra.
Affects:        All supported versions of FreeBSD.
Corrected:      2011-05-28 00:58:19 UTC (RELENG_7, 7.4-STABLE)
                2011-05-28 08:44:39 UTC (RELENG_7_3, 7.3-RELEASE-p6)
                2011-05-28 08:44:39 UTC (RELENG_7_4, 7.4-RELEASE-p2)
                2011-05-28 00:33:06 UTC (RELENG_8, 8.2-STABLE)
                2011-05-28 08:44:39 UTC (RELENG_8_1, 8.1-RELEASE-p4)
                2011-05-28 08:44:39 UTC (RELENG_8_2, 8.2-RELEASE-p2)
CVE Name:       CVE-2011-1910

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

I.   Background

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

DNS Security Extensions (DNSSEC) provides data integrity, origin
authentication and authenticated denial of existence to resolvers.

II.  Problem Description

Very large RRSIG RRsets included in a negative response can trigger
an assertion failure that will crash named(8) due to an off-by-one error
in a buffer size check.

III. Impact

If named(8) is being used as a recursive resolver, an attacker who
controls a DNS zone being resolved can cause named(8) to crash,
resulting in a denial of (DNS resolving) service.

DNSSEC does not need to be enabled on the resolver for it to be

IV.  Workaround

No workaround is available, but systems not running the BIND DNS server
or using it exclusively as an authoritative name server (i.e., not as a
caching resolver) are not vulnerable.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE,
or to the RELENG_8_2, RELENG_8_1, RELENG_7_4, or RELENG_7_3
security branch dated after the correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to FreeBSD
7.3, 7.4, 8.1 and 8.2 systems.

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

# fetch
# fetch

b) Execute the following commands as root:

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

3) To update your vulnerable system via a binary patch:

Systems running 7.3-RELEASE, 7.4-RELEASE, 8.1-RELEASE, or 8.2-RELEASE
on the i386 or amd64 platforms can be updated via the freebsd-update(8)

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

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


Branch                                                           Revision
- -------------------------------------------------------------------------
  src/UPDATING                                             1.507.
  src/UPDATING                                             1.507.
  src/UPDATING                                             1.632.
  src/UPDATING                                             1.632.
- -------------------------------------------------------------------------


Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/7/                                                         r222399
releng/7.4/                                                       r222416
releng/7.3/                                                       r222416
stable/8/                                                         r222396
releng/8.2/                                                       r222416
releng/8.1/                                                       r222416
head/                                                             r222395
- -------------------------------------------------------------------------

VII. References

The latest revision of this advisory is available at
Version: GnuPG v1.4.9

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