ISC has learned of the potential for an error condition in BIND 9
that can cause a nameserver to terminate with an assertion failure
when processing queries if it has been configured to use both DNS64
and Response Policy Zones (RPZ).
CVE: CVE-2012-5689
Document Version: 2.0
Posting date: 24 January 2013
Program Impacted: BIND 9
Versions affected: 9.8.0-9.8.4-P1, 9.9.0-9.9.2-P1
Severity: Low
Exploitable: Remotely
Description:
An error condition may occur when a nameserver which is configured
to use DNS64 performs a lookup for a record with an A record
rewrite rule in a Response Policy Zone (RPZ.) If the RPZ is
unable to provide a record for the name, but does provide
a rewritten A record, then the DNS64 processing code will attempt
to remap that A record into a record. Due to a coding
error, this interaction between the RPZ database and the DNS64
remapping code can cause the named process to terminate with an
assertion failure.
ISC believes the number of deployed systems that are using RPZ
rewrite rules and also using DNS64 is extremely small; furthermore,
the problem has an easy workaround (see below). However, ISC
policy calls for disclosure of any potential vulnerability in
BIND 9, regardless of how rarely the conditions for such a
vulnerability may occur in production environments. Thus, despite
the CVSS score, we assess the severity as Low, and will integrate
the bug fix into the next beta release of the affected versions.
No security patch release versions are planned, as the workaround
is simple and affords complete protection.
To prevent accidental exposure of those using these features in
combination, future versions of BIND 9 will include code to
prevent any exploitation of this bug, beginning with beta versions
scheduled to be released on January 24, 2013. However, the
suggested workaround is a complete remedy for those who are using
DNS64 in conjunction with RPZ, and is recommended in preference
to running beta code in a production environment.
Impact:
Only nameservers that are configured to use both DNS64 and
Response Policy Zones, and which are maintaining A rewrite rules
but not rewrite rules, will be affected by this problem -
in other words, only systems that are using RPZ to rewrite DNS
records into A records, then attempting to remap those same A
records into via DNS64. Systems that only use RPZ to
generate NXDOMAIN or CNAME or NOERROR/NODATA responses, or to
rewrite other resource record types besides A, will not trigger
the bug.
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?calculatoradvversion=2vector=(AV:N/AC:L/Au:N/C:N/I:N/A:C)
Workaround:
If using DNS64 and Response Policy Zones together, make sure the
RPZ contains a rewrite rule for every A rewrite rule. If
the RPZ provides a answer without the assistance of DNS64,
the bug is not triggered.
Active exploits:
None
Solution:
If you are currently running one of the affected versions, you
have the following options:
1. Employ the workaround (see above).
2. Wait for BIND releases that include a fix preventing
possible exploitation of the bug.
Acknowledgements:
ISC would like to thank Pories Ediansyah of Institut Teknologi
Bandung for bringing this defect to our attention.
Document Revision History:
1.0 - 17 January 2013 Advance Notification to Phase One.
1.1 - 23 January 2013 Notification to Phase Two and Phase Three
2.0 - 24 January 2013 Notification to Phase Four (Public)
Related Documents:
See our BIND Security Matrix for a complete listing of Security
Vulnerabilities and versions affected.
https://www.isc.org/software/bind/security/matrix
If you'd like more information on our Forum or product support
please visit www.isc.org/software/guild or www.isc.org/support.
Do you still have questions? Questions regarding this advisory
should go to security-offi...@isc.org
Note: ISC patches only currently supported versions:
http://www.isc.org/software/bind/versions. When possible we
indicate EOL versions affected.
ISC Security Vulnerability Disclosure Policy:
Details of our current security advisory policy and practice can
be found at: https://www.isc.org/security-vulnerability-disclosure-policy
This Knowledge Base article https://kb.isc.org/article/AA-00855 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-2012-5689.
Legal Disclaimer:
Internet Systems Consortium (ISC) is providing this notice on
an
