cis-bind9-v301-3-4

name	cis-bind9-v301-3-4
description	Restrict Queries of the Cache (Automated)
category	cis-bind
version	3.0.1
author	cyberstrike-official
tags	["cis","bind","dns","isc-bind","bind9","restricting-queries"]
cis_id	3.4
cis_benchmark	CIS ISC BIND DNS Server 9.9 Benchmark v3.0.1
tech_stack	["bind","isc-bind","dns","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS 3.4 — Restrict Queries of the Cache

Profile Applicability

• Level 1 - Authoritative Name Server
• Level 1 - Caching Only Name Server

Description

The BIND option allow-query-cache may be used to restrict or allow BIND to provide answers to queries from the current cache of previously resolved queries. An authoritative only name server should not allow cache queries, except from the localhost. A caching only name server should allow cache queries only from the list of authorized networks.

Rationale

Caching only name servers are critical to the security of all of the clients and servers using them, only the local authorized networks should be allowed to perform queries of the server's cache. In addition to malicious malformed queries, an attacker could use information about what is or is not in the name servers cache to help setup a DNS attack against the systems using the caching name server.

Impact

Not Applicable

Audit Procedure

From the command prompt on a Microsoft Windows or Linux client not on the authorized network, send a non-recursive DNS request for a domain name for which the server is not authoritative, as shown below.

$ nslookup -norecursion www.cisecurity.org 10.3.5.53
Server: UnKnown
Address: 10.3.5.53
*** UnKnown can't find www.cisecurity.org: Query refused

-or-

** server can't find www.cisecurity.org: REFUSED

The correct response should say REFUSED, or Query Refused as shown above. If an IP address is returned, then the server accepted the quest and returned the value from the cache. If the reply includes any of the phrases can't find or No Answer, or Server failed similar to the samples below, then the request was allowed, and the value was not in the cache.

Example of Query responses that were allowed, but not in the cache

*** Can't find www.cisecurity.org: No answer

*** UnKnown can't find www.cisecurity.org: Server failed

Remediation

Authoritative Only Name Server:

For an authoritative name, insert the following either into the global options or into every zone section.

allow-query-cache { localhost; };

Caching Only Name Server:

Use the previously defined an ACL named trusted_clients which will identify the networks which are expected to use the DNS caching server, and will be allowed to send DNS cache queries.