Date: Wed, 8 Aug 2018 21:45:43 -0800 From: Michael McNally <mcnally@....org> To: oss-security@...ts.openwall.com, isc-os-security@...ts.isc.org Cc: "security-officer@....org" <security-officer@....org> Subject: CVE-2018-5740: A flaw in the "deny-answer-aliases" feature can cause an INSIST assertion failure in named Earlier today ISC disclosed CVE-2018-5740, involving a potential denial-of-service vector in an uncommonly-used feature of BIND. Our official security advisory document is posted in the ISC Knowledge Base at this URL: https://kb.isc.org/article/AA-01639 but for your convenience the text is provided below. Patched versions of BIND are available from https://www.isc.org/downloads Michael McNally ISC Security Officer ---------- A rarely-used feature in BIND has a flaw which can cause named to exit with an INSIST assertion failure. CVE: CVE-2018-5740 Document Version: 2.0 Posting date: 08 August 2018 Program Impacted: BIND Versions affected: 9.7.0->9.8.8, 9.9.0->9.9.13, 9.10.0->9.10.8, 9.11.0->9.11.4, 9.12.0->9.12.2, 9.13.0->9.13.2 and also versions of BIND 9 Supported Preview Edition Severity: High (but only for servers on which the "deny-answer-aliases" feature is explicitly enabled) Exploitable: Remotely Description: "deny-answer-aliases" is a little-used feature intended to help recursive server operators protect end users against DNS rebinding attacks, a potential method of circumventing the security model used by client browsers. However, a defect in this feature makes it easy, when the feature is in use, to experience an INSIST assertion failure in name.c. Impact: Accidental or deliberate triggering of this defect will cause an INSIST assertion failure in named, causing the named process to stop execution and resulting in denial of service to clients. Only servers which have explicitly enabled the "deny-answer-aliases" feature are at risk and disabling the feature prevents exploitation. CVSS Score: 7.5 CVSS Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit: https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Workarounds: This vulnerability can be avoided by disabling the "deny-answer-aliases" feature if it is in use. Active exploits: No known active exploits. Solution: Most operators will not need to make any changes unless they are using the "deny-answer-aliases" feature (which is described in the BIND 9 Adminstrator Reference Manual section 6.2.) "deny-answer-aliases" is off by default; only configurations which explicitly enable it can be affected by this defect. If you are using "deny-answer-aliases", upgrade to the patched release most closely related to your current version of BIND. - 9.9.13-P1 - 9.10.8-P1 - 9.11.4-P1 - 9.12.2-P1 BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers. - 9.11.3-S3 Acknowledgements: ISC would like to thank Tony Finch of the University of Cambridge for reporting this issue. Document Revision History: 1.0 Advance Notification 31 July, 2018 2.0 Public Disclosure 08 August, 2018 Related Documents: See our BIND9 Security Vulnerability Matrix at https://kb.isc.org/article/AA-00913 for a complete listing of Security Vulnerabilities and versions affected. If you'd like more information on ISC Subscription Support and Advance Security Notifications, please visit http://www.isc.org/support/. Do you still have questions? Questions regarding this advisory should go to security-officer@....org. To report a new issue, please encrypt your message using security-officer@....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 This Knowledge Base article https://kb.isc.org/article/AA-01639 is the complete and official security advisory document. 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
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