For Ubuntu operating systems using Domain Name Servers (DNS) resolution, at least two name servers must be configured.

From Canonical Ubuntu 16.04 Security Technical Implementation Guide

Associated with: CCI-000366

SV-90551r2_rule For Ubuntu operating systems using Domain Name Servers (DNS) resolution, at least two name servers must be configured.

Vulnerability discussion

To provide availability for name resolution services, multiple redundant name servers are mandated. A failure in name resolution could lead to the failure of security functions requiring name resolution, which may include time synchronization, centralized authentication, and remote system logging.

Check content

Determine whether the Ubuntu operating system is using local or Domain Name Server (DNS) name resolution with the following command: # grep hosts /etc/nsswitch.conf hosts: files dns If the DNS entry is missing from the host’s line in the "/etc/nsswitch.conf" file, the "/etc/resolv.conf" file must be empty. If the "/etc/resolv.conf" file is not empty, this is a finding. If the DNS entry is found on the host’s line of the "/etc/nsswitch.conf" file, verify the Ubuntu operating system is configured to use two or more name servers for DNS resolution. Determine the name servers used by the system with the following command: # sudo grep nameserver /etc/resolv.conf nameserver 192.168.1.2 nameserver 192.168.1.3 If less than two lines are returned that are not commented out, this is a finding.

Fix text

Configure the Ubuntu operating system to use two or more name servers for Domain Name Server (DNS) resolution. Edit the "/etc/resolv.conf" file to uncomment or add the two or more "nameserver" option lines with the IP address of local authoritative name servers. If local host resolution is being performed, the "/etc/resolv.conf" file must be empty. An empty "/etc/resolv.conf" file can be created as follows: # echo -n > /etc/resolv.conf

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