CVE-2016-2088: A response containing multiple DNS cookies causes servers with cookie support enabled to exit with an assertion failure
Document version: 2.0
Posting date: 09 March 2016
Program impacted: BIND
Versions affected: 9.10.0 -> 9.10.3-P3
BIND 9.10 has preliminary support for DNS cookies (or source identity tokens), a proposed mechanism designed to allow lightweight transaction security between a querying party and a nameserver. An error in the BIND code implementing support for this optional feature permits a deliberately misconstructed packet containing multiple cookie options to cause named to terminate with an INSIST assertion failure in resolver.c if DNS cookie support is enabled in the server. Only servers with DNS cookie support enabled at build time can be affected by this defect; in servers which do not have DNS cookie support selected, any cookies encountered will be ignored as unknown option types.
Servers which are built with DNS cookie support enabled are vulnerable to denial of service if an attacker can cause them to receive and process a response that contains multiple cookie options.
CVSS Score: 7.8
CVSS Vector: (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: https://nvd.nist.gov/cvss.cfm?calculator&version=2&vector=(AV:N/AC:L/Au:N/C:N/I:N/A:C).
Servers which do not have cookie support included are not at risk from this vulnerability.
When BIND 9.10 is built from ISC-supported source, cookie support is not selected by default. To be included, it must be elected using the "--enable-sit" command-line argument when running the "configure" script in the top level source directory. Operators with affected servers can reconfigure and rebuild BIND without cookie support if they prefer not to upgrade to a release containing the fix. However, ISC-provided binary packages for Windows do have "--enable-sit" selected. Server operators using the Windows binary packages should upgrade to the corrected version.
Active exploits: No known active exploits.
Solution: Reconfigure and rebuild BIND without enabling cookie support or upgrade to the patched release most closely related to your current version of BIND.
- BIND 9 version 9.10.3-P4
Document Revision History:
1.0 Advance Notification 02 March 2016
2.0 Public Disclosure 09 March 2016
Related Documents: See our BIND 9 Security Vulnerability Matrix for a complete listing of Security Vulnerabilities and versions affected.
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