Forum Discussion
Blocking file uploads to all sites, unless safelisted
We're trying to verify if we can block file uploads through the browser to all sites, unless these sites are part of an approved list or the user has an exception. We currently have a similar solution through a different vendor, but wanted to see if Defender for Endpoint is an alternative.
So, if someone creates a new site, this site would not be allowed to be uploaded to unless the domain is added to an approved list. The alternative would be to block if the file has a specific label.
Thanks,
- miller34mike
Microsoft
Hi DanSec
Since you're wanting to set a "safe list" which will block uploads to anything not on this list, you'll likely want to leverage the service domains feature under Endpoint DLP settings in the Microsoft Purview portal.
You can set the service domains to be an "Allow" list to achieve this and will need an Endpoint DLP policy configure once you've set the list. The policy itself can have your specific user exclusions set (Endpoint DLP is still identity based).
While DLP is typically based on sensitive information, you can set the policy to block uploads based on file types and/or file extensions. As you mentioned, you can also scope it to block based on a specific sensitivity label applied to the file.
miller34mike, I tried creating a custom DLP policy under https://compliance.microsoft.com. Scoped it to devices and MCAS, yet I can't see any action that allows me to block the upload to the web page. What am I doing wrong?
- miller34mike
Hi The737
This is due to selecting both Devices and MDCA. When you scope to multiple locations, you only get the options that are available in both locations.
To set and Endpoint policy to block service domain uploads you will need to set the policy to Devices only and then within the rule, you will see service domain uploads.
To see this option, select actions > Audit or restrict activities on devices and it will be the first checkbox that you can select.
MDCA from a DLP perspective would not help you in this scenario.
To set your allowed list of service domains, which means everything else gets blocked, go to compliance.microsoft.com > Data loss prevention > Endpoint DLP settings and find the drop-down for Browser and domain restrictions to sensitive data. Make sure the drop-down for block/allow is set to allow and then set your appropriate sites.
- Evaluate Defender for Cloud Apps, formerly MCAS.
https://techcommunity.microsoft.com/t5/security-compliance-and-identity/block-access-to-unsanctioned-apps-with-microsoft-defender-atp/ba-p/1121179
Session policy as well as sanctioned/unsanctioned apps comes to mind. Also DLP auto labeling auto encrypt all files to a basic internal label. Users would have to authenticate with their AAD credentials to verify yes/no they have access to permissions on file for encryption.WilliamLeininger , thanks for this. I wouldn't want to classify/label documents. The endpoint should catch that the user is uploading files to a blocked website and prevent the action.
- Did you ever manage to solve this? Looking for the same thing myself.
