CVE-2011-1907: RRSIG Queries Can Trigger Server Crash When Using Response Policy Zones
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CVE-2011-1907: RRSIG Queries Can Trigger Server Crash When Using Response Policy Zones

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Article summary

RRSIG Queries Can Trigger Server Crash When Using Response Policy Zones

When a name server is configured with a response policy zone (RPZ), queries for type RRSIG can trigger a server crash.


Document Version: 1.2

Posting Date: 05 May 2011

Program ImpactedBIND

Versions Affected: 9.8.0

Severity: High

Exploitable: Remotely


This advisory only affects BIND users who are using the RPZ feature configured for RRset replacement. BIND 9.8.0 introduced Response Policy Zones (RPZ), a mechanism for modifying DNS responses returned by a recursive server according to a set of rules which are either defined locally or imported from a reputation provider. In typical configurations, RPZ is used to force NXDOMAIN responses for untrusted names. It can also be used for RRset replacement, i.e., returning a positive answer defined by the response policy. When RPZ is being used, a query of type RRSIG for a name configured for RRset replacement will trigger an assertion failure and cause the name server process to exit.

Workarounds: Install 9.8.0-P1 or higher.

Active Exploits: None. However, some DNSSEC validators are known to send type=RRSIG queries, innocently triggering the failure.

Solution: Use RPZ only for forcing NXDOMAIN responses and not for RRset replacement.

CVSS Score: Base 6.1, adjusted for lack of targets, score is 1.5 (AV:N/AC:L/Au:N/C:N/I:N/A:C/E:P/RL:O/RC:C/TD:L)

For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit:

Thank you to Mitsuru Shimamura at Internet Initiative Japan for finding this defect.

For more information about DNS RPZ, please check the following: Blocking DNS.

Do you have questions? Questions regarding this advisory should go to

Do you need software support? Questions on ISC's Support services or other offerings should be sent to More information on ISC's support and other offerings is available at:

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