cis-bind-v100-1-4

name	cis-bind-v100-1-4
description	Use Secure Upstream Caching DNS Servers (Manual)
category	cis-bind
version	1.0
author	cyberstrike-official
tags	["cis","bind","dns","isc-bind","bind9","planning-and-architecture"]
cis_id	1.4
cis_benchmark	CIS ISC BIND DNS Server 9.11 Benchmark v1.0.0
tech_stack	["bind","isc-bind","dns","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS 1.4 — Use Secure Upstream Caching DNS Servers

Profile Applicability

• Caching Only Name Server Level 2

Description

Caching name servers often forward queries to another caching name server to allow the name service work to be aggregated and improve performance by taking advantage of the cache of an upstream name server. The default caching name server provided by the Internet service provider is often used in this manner. This may also be a security weakness by relying on insecure servers outside the organization's control and security policies.

Rationale

The security of all of the external connections that your systems on your network depend in part on getting accurate IP addresses for external names. If the upstream caching name server is compromised, or has its cache poisoned with malicious records, then your entire network may be subject to an attack which may redirect web, email, or VPN traffic to malicious servers, or may cause denial of services attacks. Therefore, it is important to evaluate the security of the upstream caching name servers to reduce the risk of DNS attacks propagated to your network via the upstream provider. There are a number of security companies that offer secure caching DNS services that are worth considering. Features to look for and test include:

• Blocking of traffic to websites known to contain malware.
• Configurable categories for blocking inappropriate content, such as adult content.
• Detecting and blocking of malware communications to an external command and control server.
• Prevent DNS spoofing by ensuring the integrity and authenticity of all DNS responses.

Impact

Not specified.

Audit Procedure

Perform the following for an audit:

• Check the network architecture and the identify all internal authorized caching DNS servers configured via DHCP or statically.
• Verify that there are network firewall and access controls rules that prevent internal systems from sending DNS queries directly to unauthorized external DNS servers. Only the authorized internal DNS servers should be allowed to send external DNS queries and they should be configured to only use authorized external DNS servers. An example direct DNS query on a Microsoft Windows system can be done via nslookup, and should timeout as shown below.

C:\> nslookup cisecuritry.org 8.8.8.8
DNS request timed out.
timeout was 2 seconds.
Server: UnKnown
Address: 8.8.8.8
. . .

• Review the configuration of DNS forwarders for internal caching DNS servers to ensure the that only authorized DNS servers are configured. The following perl command maybe helpful in extracting forwarders directives from the configuration files.