Information
By default, users can install add-ins in their Microsoft Word, Excel, and PowerPoint applications, allowing data access within the application.
Do not allow users to install add-ins in Word, Excel, or PowerPoint.
Rationale:
Attackers commonly use vulnerable and custom-built add-ins to access data in user applications.
While allowing users to install add-ins by themselves does allow them to easily acquire useful add-ins that integrate with Microsoft applications, it can represent a risk if not used and monitored carefully.
Disable future user's ability to install add-ins in Microsoft Word, Excel, or PowerPoint helps reduce your threat-surface and mitigate this risk.
Impact:
Implementation of this change will impact both end users and administrators. End users will not be able to install add-ins that they may want to install.
NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.
Solution
To prohibit users installing Office Store add-ins and starting 365 trials:
Navigate to Microsoft 365 admin center https://admin.microsoft.com.
Click to expand Settings Select 'Org settings'.
Under Services select User owned apps and services.
Uncheck Let users access the Office Store and Let users start trials on behalf of your organization.
Click Save.
Default Value:
Let users access the Office Store is Checked
Let users start trials on behalf of your organization is Checked