The 'EC2 Network ACL Modified' rule is designed to detect modifications made to AWS EC2 Network Access Control Lists (ACLs). The rule leverages AWS CloudTrail logs to monitor events related to the creation of Network ACL entries. A primary focus is on the event name 'CreateNetworkAclEntry', which is triggered when a new entry is added to a Network ACL. The rule identifies modifications made by users operating under an assumed IAM role, emphasizing secure practices like multi-factor authentication (MFA). The potential severity of unauthorized modifications is reflected in the assigned severity level of 'Info', indicating that while the event itself may not indicate an immediate threat, such changes warrant monitoring to prevent potential misuse or misconfigurations that could lead to vulnerabilities. The rule includes a set of tests designed to validate the presence or absence of modifications, capturing different log scenarios that may indicate successful or failed modification attempts. The runbook provides guidance for responding to alerts generated by this rule, while referenced documentation outlines the operational thresholds and best practices for managing Network ACLs in AWS.