How to Secure Guest Sharing Without Killing Collaboration

Security
Microsoft 365

Microsoft 365’s default sharing settings are convenient but risky. They allow anyone in your company to invite guests and share potentially sensitive data, which can lead to problems like:

  • Guest sprawl: Unmanaged guest users accumulating over time.
  • Oversharing: Employees sharing more than necessary, often unintentionally.
  • Data exfiltration: Sensitive data being accessed by external users and potentially leaking.

By implementing our security framework, you’ll ensure that your environment is locked down while maintaining smooth collaboration.

Achieve Peace of Mind

With the right configuration, you can enable secure guest access without adding extra burdens to your IT team. Here’s how:

Our Framework for Secure Guest Sharing

Manage Guest Access and Lifecycle

Guests can be invited to your Microsoft 365 environment in four ways:

  1. Content Sharing (e.g., via SharePoint or OneDrive links).
  2. Self-service sign-up flows (users sign themselves up through Entra B2B).
  3. Admin Invitations (admins manually invite guests through the Entra portal).
  4. Custom invitation APIs (use APIs to onboard external users via custom processes).

After guests are invited, configure redemption flows to control how they authenticate. You can enable or disable email OTP (One-Time Passcode) for guests who don’t have access to a trusted identity provider. You can also set federation targets, which allow guests from certain trusted organizations to authenticate directly using their existing credentials, making onboarding smoother for partners.

Set Up Privacy & Consent Requirements

Before guests can access any data, require them to agree to your privacy policy and terms of use. This step ensures legal compliance and that guests acknowledge your data-sharing expectations upfront.

Strengthen Security with Conditional Access Policies

You can enforce Conditional Access policies to further restrict guest activity:

  • Session Timeouts: Configure time limits for guest sessions to minimize unauthorized lingering.
  • Web-only Access: Prevent guests from downloading or syncing files to their local devices by restricting access to web apps.
  • Trust MFA: If guests have completed multi-factor authentication (MFA) in their own organization, you can choose to trust that verification rather than requiring them to redo MFA.
  • Trust Devices: Limit access to guests who are using compliant or trusted devices, adding another layer of security.

Configure Sharing Settings in Microsoft 365

Once you’ve handled guest access, dive into Microsoft 365’s sharing settings for granular control. Here’s a breakdown:

  • Azure AD External Identities: Manage guest user accounts and set up restrictions on which domains can collaborate with your organization. You can block or allow specific external domains.
  • Microsoft 365 Admin Center: Control how external sharing works at the organizational level, whether for OneDrive, SharePoint, or Teams. You can limit external sharing to “existing guests” to prevent uncontrolled invitations.
  • Teams: Adjust guest permissions in individual Teams. For example, guests can be allowed to access channels and files but blocked from inviting new users or editing settings.
  • SharePoint: Use SharePoint site settings to control guest access for individual sites. You can restrict sharing permissions so that guests only have limited access to specific files and folders.

Implement Container/File-Level Security with Sensitivity Labels

Sensitivity labels help secure not only the content being shared but the containers themselves. Here’s how you can use them:

  • Apply sensitivity labels to Teams and SharePoint sites. This can control things such as if the container will allow guests, it’s default internal privacy settings, and some basic conditional access policies.
  • Apply sensitivity labels to individual files. This ensures that even if a file is downloaded by a guest or shared externally, the encryption and access restrictions will follow the file.

With sensitivity labels, files remain protected, even in cases of accidental oversharing. Sensitivity labels can also trigger automatic actions, such as applying encryption, watermarking, or requiring additional authentication to access highly sensitive files.