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

Note: If the system is running in a cloud platform and the cloud provider gives a single, highly available IP address for DNS configuration, this control is Not Applicable.

Verify the name servers used by the system with the following command:

$ grep nameserver /etc/resolv.conf

nameserver 192.168.1.2
nameserver 192.168.1.3

If fewer than two lines are returned that are not commented out, this is a finding.

Fix

Configure the operating system to use two or more name servers for DNS resolution based on the DNS mode of the system.

If the NetworkManager DNS mode is set to "none", add the following lines to "/etc/resolv.conf":

nameserver [name server 1]
nameserver [name server 2]

Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers.

If the NetworkManager DNS mode is set to "default", add two DNS servers to a NetworkManager connection using the following command:

$ nmcli connection modify [connection name] ipv4.dns [name server 1],[name server 2]

Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers. Replace [connection name] with a valid NetworkManager connection name on the system. Replace ipv4 with ipv6 if IPv6 DNS servers are used.