title:  An error processing RPZ rules can cause named to loop endlessly after handling a query
description: If named is configured to use Response Policy Zones (RPZ) an error processing some rule types can lead to a condition where BIND will endlessly loop while handling a query. Affects BIND 9.9.10, 9.10.5, 9.11.0->9.11.1, 9.9.10-S1, 9.10.5-S1.
problem types: A server is potentially vulnerable to degradation of service if
the server is configured to use RPZ,
the server uses NSDNAME or NSIP policy rules, and
an attacker can cause the server to process a specific query
Successful exploitation of this condition will cause named to enter a state where it continues to loop while processing the query without ever reaching an end state. While in this state, named repeatedly queries the same sets of authoritative nameservers and this behavior will usually persist indefinitely beyond the normal client query processing timeout. By triggering this condition multiple times, an attacker could cause a deliberate and substantial degradation in service.
Operators of servers that meet the above conditions 1. and 2. may also accidentally encounter this defect during normal operation.  It is for this reason that the decision was made to issue this advisory despite its low CVSS score.
affected:
{
product: BIND 9
vendor: ISC
versions:
status: affected, version: 9.9.10, 9.10.5, 9.11.0->9.11.1, 9.9.10-S1, 9.10.5-S1
}
metrics:
cvssV3_0: [
attackComplexity: HIGH
attackVector: NETWORK
availabilityImpact: LOW
baseScore: 3.7
baseSeverity: LOW
confidentialityImpact: NONE
integrityImpact: NONE
privilegesRequired: NONE
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
version: 3.0
]
solutions: 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.
BIND 9 version 9.9.10-P1
BIND 9 version 9.10.5-P1
BIND 9 version 9.11.1-P1
BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.
BIND 9 version 9.9.10-S2
BIND 9 version 9.10.5-S2
workarounds: Only the NSDNAME and NSIP RPZ rule types can cause this condition to occur.  You can work around this vulnerability if you are able to express your desired policy while avoiding NSDNAME or NSIP rules, otherwise it is advised that you upgrade to a version which corrects the defect.