How to Lock Down Microsoft Teams: A Security Guide for Businesses

Teams isn't just a chat app — it's a security surface

Microsoft Teams is the most widely used collaboration tool across businesses running Microsoft 365. But most organizations treat it as a simple chat application without considering that Teams has direct access to SharePoint, OneDrive, email, and often third-party applications.

When someone creates a Team, Microsoft 365 automatically provisions a security group, a SharePoint site, a shared mailbox, and a OneDrive folder. If you don't control who can create Teams and what permissions they have, you're opening invisible doors to your data.

The 7 most common Teams security risks

1. Anyone can create Teams

By default, all users can create new Teams. In organizations with 200+ employees, this results in dozens of abandoned Teams with sensitive documents and no responsible owner.

Fix: Restrict Team creation to a specific Azure AD group. Employees request new Teams through an approval workflow.

2. Unrestricted guest access

Default settings allow any user to invite external people to any Team. A vendor invited to a "Logistics" Team can see every SharePoint file associated with that Team.

Fix: Disable guest access globally and enable it only for specific Teams where external access is justified and approved.

3. Uncontrolled file sharing

Files shared in Teams are stored in SharePoint. If SharePoint sharing policies allow "anyone with the link," a confidential file shared in a Teams chat can end up indexed by search engines.

Fix: Configure SharePoint to allow only "people in your organization" sharing by default. Enable external sharing only on specific sites with business justification.

4. Unreviewed third-party apps

Teams allows installation of third-party apps (bots, connectors, tabs) that can access Team data. Without restrictions, an employee can install an unvetted app that exfiltrates data.

Fix: Block third-party app installation by default. Create an allow-list of IT-approved apps.

5. Meeting recordings accessible to everyone

Teams meeting recordings are stored in the organizer's OneDrive (for regular meetings) or SharePoint (for channel meetings). Without proper permissions, anyone with the link can view recordings — including executive meetings.

Fix: Configure meeting policies to restrict who can record and where recordings are stored. Apply sensitivity labels to executive meeting recordings.

6. Chat messages without retention

By default, Teams chat messages have no retention policy. Sensitive data shared in chat (passwords, account numbers, contracts) persists indefinitely without governance.

Fix: Apply Teams retention policies in the Compliance Center. Define retention periods based on content classification.

7. No DLP configured

Microsoft 365 includes DLP (Data Loss Prevention) that can detect when someone shares credit card numbers, tax IDs, or other sensitive information in Teams. Most companies never configure it.

Fix: Enable DLP policies for Microsoft Teams that detect and block sharing of sensitive data types relevant to your business.

Teams security checklist

• [ ] Team creation restricted to authorized group
• [ ] Guest access disabled by default
• [ ] SharePoint external sharing limited to approved domains
• [ ] Third-party apps blocked except allow-listed ones
• [ ] Meeting policies configured (recording, lobby, anonymous participants)
• [ ] Retention policies for chats and channel messages
• [ ] DLP enabled for sensitive data types
• [ ] Quarterly review of inactive Teams (archive or delete)

How to assess your current configuration

You don't need to review every setting manually. Our free scan evaluates the 155 Microsoft Graph rules of the 201-rule library against your Microsoft 365 tenant, including Teams configuration, guest policies, external sharing, and DLP settings. You get a complete diagnostic in 90 seconds. The 46 Azure Resource Manager controls add on with admin consent.

Scan your Teams setup for free →