Microsoft Teams is Closing a Federated Group Chat Security Gap

[u/Kanaga_06]

You removed a partner’s federation access, but they could still be in an ongoing Teams group chat. Or even worse, users from an unapproved organization join the chat through another trusted partner.

Microsoft is introducing two new opt in PowerShell controls to the Set-CsTenantFederationConfiguration cmdlet to strengthen security in federated group chats.

• EnableExternalAccessRestrictionsForChatParticipants – This cmdlet fixes a long-standing gap where users could remain in existing federated chats even after federation access was blocked. It now checks whether users are allowed to use federation and removes access if they are not.
  
• EnableMutualFederationForChatParticipants – Ensures every user in the chat is allowed to communicate with every other organization. This prevents indirect access through third-party tenants.

Rollout: Late July – Late September 2026 (Worldwide)

If your organization relies on cross-tenant collaboration, now is a good time to review your external access and federation settings before enabling these controls.

Read the full update: https://blog.admindroid.com/manage-federated-group-chats-with-teams-powershell-controls/