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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2018.0755 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) Windows Impact/Access: Reduced Security -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2017-3143 Reference: ESB-2018.0216 ESB-2017.2228 ESB-2017.1861 ESB-2017.1640.3 ESB-2017.1638 Original Bulletin: https://kb.isc.org/article/AA-01599/0/Operational-Notification%3A-update-policy-local-was-named-misleadingly-and-could-permit-non-local-DDNS-updates.html - --------------------------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, 9.12.0->9.12.0-P1 Description: "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 locally. 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. Impact: 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. Workarounds: 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; };" Solution: Software versions which enforce the corrected, more restrictive behavior are now available from our downloads page, http://www.isc.org/downloads/all. - 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: https://www.isc.org/downloads/software-support-policy/openpgp-key/. If you are unable to use encrypted email, you may also report new issues at: https://www.isc.org/community/report-bug/. Note: ISC patches only currently supported versions. When possible we indicate EOL versions affected. (For current information on which versions are actively supported, please see http://www.isc.org/downloads/). 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 bind-announce@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-announce - --------------------------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: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane 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). 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