7.2.6 Ensure SharePoint external sharing is managed through domain whitelist/blacklists

Information

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 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 provided the target output to assist in reviewing the benchmark to ensure target compliance.

Solution

To remediate using the UI:

Navigate to SharePoint admin center https://admin.microsoft.com/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 remediate using PowerShell:

Connect to SharePoint Online using Connect-SPOService.

Run the following PowerShell command:

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

Default Value:

Limit external sharing by domain is unchecked

SharingDomainRestrictionMode: None

SharingDomainRestrictionMode: <Undefined>

See Also

https://workbench.cisecurity.org/benchmarks/15279

Item Details

Category: ACCESS CONTROL, MEDIA PROTECTION

References: 800-53|AC-3, 800-53|AC-5, 800-53|AC-6, 800-53|MP-2, CSCv7|13.4, CSCv7|14.6

Plugin: microsoft_azure

Control ID: 30bc5e9c7706c03c3f05a12fc2e71f0aa9a6a4c91c9061fd151f6f0e53e2d1c8