6.1 Ensure document sharing is being controlled by domains with whitelist or blacklist

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Information

You should control sharing of documents to external domains by either blocking domains or only allowing sharing with specific named domains.

Rationale:

Attackers will often attempt to expose sensitive information to external entities through sharing, and restricting the domains that your users can share documents with will reduce that surface area.

Impact:

Enabling this feature will prevent users from sharing documents with domains outside of the organization unless allowed.

NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.

Solution

To configure document sharing restrictions, use the Microsoft 365 Admin Center:

Navigate to Microsoft 365 administration portal (https://admin.microsoft.com), Click on Admin Centers and then SharePoint.

Expand Policies then click Sharing.

Expand More external sharing settings and check Limit external sharing by domain.

Select Add domains to add a list of approved domains

Click Save at the bottom of the page.

To configure document sharing restrictions, you can also use SharePoint Online PowerShell:

Connect to SharePoint Online using Connect-SPOService

Run the following PowerShell command:

Set-SPOTenant -SharingDomainRestrictionMode AllowList -SharingAllowedDomainList 'domain1.com domain2.com'

Default Value:

off

See Also

https://workbench.cisecurity.org/files/3729