CVE-2018-5740: A flaw in the "deny-answer-aliases" feature can cause an assertion failure in named
A rarely-used feature in BIND has a flaw which can cause named to exit with an assertion failure.
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
Severity: High (but only for servers on which the "deny-answer-aliases" feature is explicitly enabled)
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 assertion failure in name.c.
Impact: Accidental or deliberate triggering of this defect will cause a REQUIRE 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.
BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.
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
2.1 Initial text incorrectly described the failed assertion as an INSIST (rather than REQUIRE) assertion 09 August, 2018
Related Documents: See our BIND 9 Security Vulnerability Matrix 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 https://www.isc.org/support/.
Do you still have questions? Questions regarding this advisory should go to firstname.lastname@example.org. To report a new issue, please encrypt your message using email@example.com'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 https://www.isc.org/downloads/).
ISC Security Vulnerability Disclosure Policy: Details of our current security advisory policy and practice can be found in the ISC Software Defect and Security Vulnerability Disclosure Policy.
This Knowledgebase article is the complete and official security advisory document.
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.