Microsoft Graph API Inbox Enumeration
This rule identifies enumeration of user inboxes within an Entra ID tenant via the Microsoft Graph API. It specifically looks for multiple GET requests to the `/v1.0/users/*/mailFolders/Inbox/messages` endpoint from a single IP address and session within a 5-minute window. The detection is based on the behavior of tools like Invoke-GraphOpenInboxFinder in GraphRunner, but is applicable to any tool performing similar inbox scanning. The rule provides outcomes detailing the number of scanned users, successful accesses (HTTP 200), forbidden accesses (HTTP 403), and not found inboxes (HTTP 404).
YARA-L
