A specific query can cause BIND nameservers using DNS64 to exit with a REQUIRE assertion failure.
Posting date: 04 Dec 2012
BIND 9 nameservers using the DNS64 IPv6 transition mechanism are vulnerable to a software defect that allows a crafted query to crash the server with a REQUIRE assertion failure. Remote exploitation of this defect can be achieved without extensive effort, resulting in a denial-of-service (DoS) vector against affected servers.
Please Note: Support for DNS64 was added to BIND 9 in version 9.8.0. Therefore BIND 9 versions prior to 9.8.0 cannot be affected by this bug. Also, nameservers running versions 9.8.0 and greater can only be affected if DNS64 is turned on using the "dns64" configuration statement. If you are not using DNS64 you are not at risk.
For current information on which versions are actively supported, please see http://www.isc.org/software/bind/versions.
Any BIND 9 nameserver configured to use DNS64 is vulnerable to this defect and can be crashed by any client machine from which it accepts queries.
CVSS Score: 7.8
CVSS Equation: (AV:N/AC:L/Au:N/C:N/I:N/A:C)
For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit: http://nvd.nist.gov/cvss.cfm?calculator&adv&version=2&vector=(AV:N/AC:L/Au:N/C:N/I:N/A:C)
Only BIND 9 servers which are configured to use DNS64 are vulnerable. For those servers, disallowing queries from untrusted clients (a recommended practice in any case) will slightly mitigate a server's exposure, but no workarounds are available which will completely protect an affected server against exploitation of this bug. If you are using DNS64 either disable it or upgrade to a fixed version.
No known active exploits.
Solution: Upgrade to the patched release most closely related to your current version of BIND. These can all be downloaded from http://www.isc.org/downloads/all.
- BIND 9 version 9.8.4-P1
- BIND 9 version 9.9.2-P1
Acknowledgements: ISC would like to thank BlueCat Networks for bringing this defect to our attention.
Document Revision History:
1.0 - 27 November 2012 Advance Notification to Phase One.
1.1 - 03 December 2012 Notification to Phase Two and Phase Three
2.0 - 04 December 2012 Notification to Phase Four (Public)
Japanese Translation: https://kb.isc.org/article/AA-00832
Spanish Translation: https://kb.isc.org/article/AA-00834
German Translation: https://kb.isc.org/article/AA-00833
See our BIND Security Matrix for a complete listing of Security Vulnerabilities and versions affected.
If you'd like more information on our Forum or product support please visit www.isc.org/software/guild
Do you still have questions? Questions regarding this advisory should go to firstname.lastname@example.org
ISC Security Vulnerability Disclosure Policy: Details of our current security advisory policy and practice can be found here: https://www.isc.org/security-vulnerability-disclosure-policy
This Knowledge Base article https://kb.isc.org/article/AA-00828 is the complete and official security advisory document. There is also a summary article located on our website and linking to here: https://www.isc.org/software/bind/advisories/cve-2012-5688
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