The 'AWS IAM User Addition to Group' rule is designed to detect the addition of users to specified groups in AWS Identity and Access Management (IAM). The rule filters for logs related to the AWS CloudTrail service, specifically looking for successful operations of adding a user to a group (event.action: AddUserToGroup) within the IAM provider (event.provider: iam.amazonaws.com). It operates on logs indexed in the specified Filebeat and AWS CloudTrail indices within the last 60 minutes and checks these at 10-minute intervals. With a low severity and a risk score of 21, it aims to help identify potentially unauthorized changes made to user group memberships, which can be indicative of credential access-related attacks or persistence tactics as outlined in the MITRE ATT&CK framework. The rule includes guidance on triaging alerts, false positive analysis, and response strategies, aiming to improve detection and response to suspicious IAM activities within an organization's AWS environment.