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

Determine whether the system is using local or DNS name resolution with the following command:

$ sudo 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.

Verify the "/etc/resolv.conf" file is empty with the following command:

$ sudo ls -al /etc/resolv.conf

-rw-r--r-- 1 root root 0 Aug 19 08:31 resolv.conf

If local host authentication is being used and 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 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

Configure the operating system to use two or more name servers for DNS resolution.

By default, "NetworkManager" on RHEL 8 dynamically updates the /etc/resolv.conf file with the DNS settings from active "NetworkManager" connection profiles. However, this feature can be disabled to allow manual configurations.

If manually configuring DNS, 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:

$ sudo echo -n > /etc/resolv.conf