https://www.bleepingcomputer.com/news/security/new-microsoft-azure-ad-cts-feature-can-be-abused-for-lateral-movement/

Microsoft's new Azure Active Directory Cross-Tenant Synchronization (CTS) feature, introduced in June 2023, has created a new potential attack surface that might allow threat actors to more easily spread laterally to other Azure tenants.

Microsoft tenants are client organizations or sub-organizations in Azure Active Directory that are configured with their own policies, users, and settings.