The rule 'AWS.VPC.UnapprovedOutboundDNS' is designed to monitor and alert on outbound DNS traffic from AWS VPC that is directed to non-approved DNS servers. This control is crucial as unauthorized DNS traffic can indicate potential data exfiltration or a command-and-control scenario in a compromised environment. The rule utilizes AWS VPC Flow Logs and OCSF Network Activity logs, assessing DNS traffic against a set of predefined conditions that identify whether the destination IP address is approved for DNS resolution. The severity of this rule is marked as medium, highlighting its importance while not posing an immediate critical risk. It provides a direct reference to AWS documentation for flow logs, signifying the importance of DNS security within the AWS environment. Failure to adhere to approved configurations may necessitate investigation of potential malicious activity related to the outbound DNS traffic detected.