Blocking
downloads or at least blocking them on unmanaged devices is a common
requirement in the context of Microsoft Teams and SharePoint. Different
features can be used to implement such requirements.
App Enforced Restrictions
Generally, these settings can be configured in the SharePoint Admin Center:If
this setting is used, the system automatically creates two conditional access
policies in Azure AD:
These policies
can be customized and thus also used as a starting point for a more detailed
conditional access policy that, for example, only applies to selected users or
groups.
The first
screenshot above also shows the following message: We will automatically change
the "Apps that don't use modern authentication" setting to block
access (because these apps can't enforce this device-based restriction). The
background is that apps that do not use modern authentication cannot enforce
any device-based setting. If such apps remain allowed, the created conditional
access policies can be bypassed.
Another
information in the screenshot above makes clear that not all detailed settings
are available via the UI in the SharePoint Admin Center: "If you don't
want to limit or block access organization-wide, you can do so for specific
sites". The link behind "Learn how" is to the documentation of
the options via PowerShell.
Example: Set-SPOSite -Identity
https://<SharePoint online URL>/sites/<name of site or OneDrive
account> -ConditionalAccessPolicy AllowLimitedAccess
Options with Sensitivity Label
The solution via Sensitivity Label means that the settings in the SharePoint Admin Center are no longer used. The label offers the same options as for example "Allow limited, web-only access":This
setting has the following effect both in the SharePoint Admin Center and in the
label configuration:
Users
on unmanaged devices can only access the designated website through the
browser, without being able to download, print, or sync files. They also cannot
access content through apps, including Office desktop apps.
In
this scenario, the corresponding label is assigned to one or more SharePoint
sites. The label then enforces the configured setting. If the label and the settings
in the SharePoint Admin Center conflict, the label wins.
With
both options, it is thus possible to prevent downloading content from pages
explicitly configured using PowerShell or labeled with a sensitivity label that
enforces web-only access. It may take 5-10 minutes for the policy to take
effect. It will not take effect for users who are already signed in from
unmanaged devices.
Limitations of the solution with App Enforced Restrictions
The following restrictions apply when using App
Enforced Restrictions:
- If you limit access on unmanaged devices, users on managed devices must use one of the supported OS and browser combinations, or they will also have limited access.
- If you limit access and edit a site from an unmanaged device, image web parts won't display images that you upload to the site assets library or directly to the web part.
- If you're using classic SharePoint site templates, site images may not render correctly. This is because the policy prevents the original image files from being downloaded to the browser.
- When Access Control for Unmanaged Devices in SharePoint is set to Allow limited, web-only access, SharePoint files cannot be downloaded but they can be previewed. The previews of Office files work in SharePoint but the previews do not work in Microsoft Yammer.
Use Conditional Access App Control
To create rules more granular / with advanced options, "Block Download" can also be enforced with Cloud App Security. This is done by using the "Conditional Access App Control" options in Conditional Access in Azure AD:Cloud
App Security then acts as a broker that is in front of the access to Office
365:
This also
allows scenarios such as assigning a sensitivity label as soon as a document is
downloaded.
- Add file filters to the policy: Extension, File Name, File Size, Sensitivity Label
- Inspection Method: Can be used to configure include or exclude conditions
- Actions: Block, Protect (Apply sensitivity label to downloads & monitor all activities), require step-up authentication like MFA etc.,
- Configure Alerts
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