The 'GCP Firewall Rule Modified' detection rule monitors for modifications made to Google Cloud Platform (GCP) firewall rules, which are crucial for enforcing networking security policies. This rule listens specifically for changes logged in GCP's audit logs, which track operations related to firewall configuration changes. When modifications occur—such as updates to firewall rules—an alert is triggered. The rule is designed to ensure that any unexpected changes to firewall configurations are reviewed, as these could lead to service interruptions or potential security vulnerabilities. Alerts are generated on specific API calls, including firewall updates and modifications made through various services like App Engine. The severity of the alerts is classified as low, but they are essential for maintaining secure infrastructure management in GCP environments.