RHEL 9 must configure a DNS processing mode in Network Manager.

To ensure that DNS resolver settings are respected, a DNS mode in Network Manager must be configured. The following are common DNS values in NetworkManager.conf [main]:

- default: NetworkManager will update /etc/resolv.conf to reflect the nameservers provided by currently active connections. - none: NetworkManager will not modify /etc/resolv.conf. Used when DNS is managed manually or by another service. - systemd-resolved: Uses systemd-resolved to manage DNS. - dnsmasq: Enables the internal dnsmasq plugin.

Verify that RHEL 9 has a DNS mode configured in Network Manager.

$ NetworkManager --print-config [main] dns=none

If the dns key under main does not exist or is not set to "default", "none", or "systemd-resolved", this is a finding.

Note: If RHEL 9 is configured to use a DNS resolver other than Network Manager, the configuration must be documented and approved by the information system security officer (ISSO).

Configure NetworkManager in RHEL 9 to use a DNS mode.

In "/etc/NetworkManager/NetworkManager.conf", add the following line in the "[main]" section:

dns = <dns processing mode>

Where <dns processing mode> is default, none, or systemd-resolved.

NetworkManager must be reloaded for the change to take effect.

$ sudo systemctl reload NetworkManager