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

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-257949	SRG-OS-000480-GPOS-00227	RHEL-09-252040	SV-257949r1134947_rule	2025-11-24	2

Description
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.

Description

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.

ℹ️ Check
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).

ℹ️ Check

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).

✔️ Fix
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