This detection rule identifies potential Kerberos ticket forgery attacks, specifically focusing on the Diamond Ticket attack. It does so by analyzing Windows Security Event Log 4627 events that log account logon activities. The key detection mechanism involves the GroupMembership field in event 4627, which indicates a user's group memberships at the time of login. If a user logs in and the GroupMembership indicates they belong to a privileged group such as 'Domain Admins', but they are not actually part of that group according to the directory service, this discrepancy raises a flag for potential ticket forging. The rule utilizes a lookup table that must be diligently maintained and updated to accurately reflect actual group memberships. If the user's reported membership differs from what is stored in the lookup, this could signify an ongoing ticket forging attack. Such attacks enable attackers to impersonate users and exploit privileges without authorization, allowing for unauthorized resource access. Monitoring these discrepancies during logon events is critical for indicating possible malicious activity, making it essential for security teams to investigate any alerts triggered by this detection.