Hash: SHA256

             AUSCERT External Security Bulletin Redistribution

         Operational Notification: "update-policy local" was named
           misleadingly and could permit non-local DDNS updates
                               16 March 2018


        AusCERT Security Bulletin Summary

Product:           BIND
Publisher:         ISC
Operating System:  UNIX variants (UNIX, Linux, OSX)
Impact/Access:     Reduced Security -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2017-3143  

Reference:         ESB-2018.0216

Original Bulletin: 

- --------------------------BEGIN INCLUDED TEXT--------------------

Posting date:        14 March 2018
Program Impacted:    BIND
Versions affected:   9.0.x -> 9.8.x, 9.9.0->9.9.11-P1,
                     9.10.0->9.10.6-P1, 9.11.0->9.11.2-P1,

   "update-policy local;", which is a permission cluster provided
   as a shortcut for operators who use Dynamic DNS (DDNS), was
   misleadingly named in that its original implementation did not
   actually enforce a requirement that the updates it allows originate

   A full description of "update-policy local;" is included in
   Section 6.2 of the BIND Administrator Reference Manual, but to
   briefly summarize:

      When "update-policy local;" is set for a zone in named.conf,
      named will create and use an automatically generated session
      key (named "local-ddns" by default and stored in local storage
      on the server) and will permit updates to the zone to any
      client successfully authenticating using that key.

      Since the key is generated and stored locally, in usual cases
      this should equate to only allowing local updates unless an
      operator deliberately copies the local-ddns key elsewhere.

   However, in June 2017 disclosed CVE-2017-3143, a flaw in TSIG
   authentication which enabled an attacker who was able to send
   and receive messages to an authoritative DNS server and who had
   knowledge of a valid TSIG key name for the zone and service being
   targeted to manipulate BIND into accepting an unauthorized dynamic
   update.  In our disclosure for CVE-2017-3143 we warned of its
   potential interaction with the behavior of update-policy local.
   By policy, however, ISC prefers security releases to contain
   only the minimal fix required to prevent the exploitable condition.
   Therefore, security patch releases for CVE-2017-3143 fixed only
   the TSIG authentication flaw without changing the behavior of
   the "update-policy local;" feature.

   Beginning with the March 2018 maintenance releases of BIND
   (9.9.12, 9.10.7, 9.11.3, and 9.12.1) the behavior of "update-policy
   local" is now changed so that updates are permitted under the
   policy only when they are received from locally configured
   addresses AND use the local session key.


   We think it is unlikely that many operators are deliberately
   relying on the non-local option of the previous behavior (and
   we recommend against it) but if any are, please see the "Workarounds"
   section of this advisory for advice on how to replicate the
   previous behavior.  For all other operators (those who were not
   relying on the non-local side-effect of the previous behavior)
   the new behavior should represent an improvement in DDNS security
   if you use the local update policy.


   The change in "update-policy local;" behavior which debuts in
   the March 2018 maintenance releases should improve security by
   properly restricting updates to only those that are received
   from locally configured addresses AND are authenticated using
   the local session key.  However, in the event that an operator
   was deliberately relying on the non-local option of the previous
   behavior, behavior equivalent to the previous behavior of
   "update-policy local;" can be produced by using this syntax:
   "update-policy { grant local-ddns zonesub any; };"


   Software versions which enforce the corrected, more restrictive
   behavior are now available from our downloads page,

   - BIND 9 version 9.9.12
   - BIND 9 version 9.10.7
   - BIND 9 version 9.11.3
   - BIND 9 version 9.12.1

Do you still have questions?  Questions regarding this advisory
should go to security-officer@isc.org.  To report a new issue,
please encrypt your message using security-officer@isc.org's PGP
key which can be found here:
If you are unable to use encrypted email, you may also report new
issues at: https://www.isc.org/community/report-bug/.


   ISC patches only currently supported versions. When possible we
   indicate EOL versions affected.  (For current information on
   which versions are actively supported, please see

ISC Security Vulnerability Disclosure Policy:

   Details of our current security advisory policy and practice can
   be found here: https://kb.isc.org/article/AA-00861

Legal Disclaimer:

   Internet Systems Consortium (ISC) is providing this notice on
   an "AS IS" basis. No warranty or guarantee of any kind is expressed
   in this notice and none should be implied. ISC expressly excludes
   and disclaims any warranties regarding this notice or materials
   referred to in this notice, including, without limitation, any
   implied warranty of merchantability, fitness for a particular
   purpose, absence of hidden defects, or of non-infringement. Your
   use or reliance on this notice or materials referred to in this
   notice is at your own risk. ISC may change this notice at any
   time.  A stand-alone copy or paraphrase of the text of this
   document that omits the document URL is an uncontrolled copy.
   Uncontrolled copies may lack important information, be out of
   date, or contain factual errors.

(c) 2001-2018 Internet Systems Consortium
bind-announce mailing list

- --------------------------END INCLUDED TEXT--------------------

You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.

NOTE: Third Party Rights
This security bulletin is provided as a service to AusCERT's members.  As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.

NOTE: This is only the original release of the security bulletin.  It may
not be updated when updates to the original are made.  If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.

Contact information for the authors of the original document is included
in the Security Bulletin above.  If you have any questions or need further
information, please contact them directly.

Previous advisories and external security bulletins can be retrieved from:


Australian Computer Emergency Response Team
The University of Queensland
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
Comment: http://www.auscert.org.au/render.html?it=1967