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V-258898

CAT II (Medium)

The Photon operating system must disable systemd fallback DNS.

Rule ID

SV-258898r935569_rule

STIG

VMware vSphere 8.0 vCenter Appliance Photon OS 4.0 Security Technical Implementation Guide

Version

V1R1

CCIs

CCI-000366

Discussion

Systemd contains an ability to set fallback DNS servers, which is used for DNS lookups in the event no system level DNS servers are configured or other DNS servers are specified in the Systemd resolved.conf file. If uncommented, this configuration contains Google DNS servers by default and could result in DNS leaking info unknowingly in the event DNS is absent or misconfigured at the system level.

Check Content

At the command line, run the following command to verify systemd fallback DNS is disabled:

# resolvectl status | grep '^Fallback DNS'

If the output indicates that Fallback DNS servers are configured, this is a finding.

Fix Text

Navigate to and open:

/etc/systemd/resolved.conf

Add or update the "FallbackDNS" entry to the following:

FallbackDNS=

Restart the Systemd resolved service by running the following command:

# systemctl restart systemd-resolved

Note: If this option is not given, a compiled-in list of DNS servers is used instead, which is undesirable.