Microsoft Teams tenant specific DLP

[WillNunez]

We are a defence company and have protective labels on our documents.

We have endpoint DLP to ensure that protectively marked documents are not uploaded to services that they shouldnt be.

We are now in a position where we can store these documents in our tenant but would like to block upload to 3rd party tenants.

URLs do not include the tenant name si we cant use URL filtering on our endpoint DLP or proxy.

Ive been told it can be done using CASB. Ive been looking at Microsoft Cloud defender as a CASB but am struggling to find out how to do it.

So questions:

1) Tenancy specific DLP. Is CASB the answer ?

2) If it is can microsoft cloud defender be used? (Forcepoint claim their CASB can yet Microsoft seems to score higher with Gartner)

3) if the answer to 1 and 2 is yes....can anyone sign post me on how to do it?

[#2]

Wouldn't protecting said documents via a sensitivity label/RMS encryption be a better solution? You can define domain-based protection if needed, and you can integrate it with the DLP controls too.

[#3]

We use labels and resources is on the roadmap. However some labels have a classification which means they cannot be stored in cloud that hasn't been accredited

Endpoint dlp can prevent application and url level uploading. But with teams for example you can't differentiate between tenancies by url. I want to be able to block uploads of classified files at a tenancy level. I've been told casb by other vendors can do this. I'm trying to work out how it can be done with microsoft

[#4]

You can use CA with a Conditional Access App Control session policy, connected to Microsoft Defender for Cloud Apps, with the session control type "Control file upload" and action "Block". There are many configuration options in there, such as scoping on sensitivity labels etc., and target "All company" for example.

Not sure you've seen the new setting in Endpoint DLP for devices where you can select a block of upload if a document isn't already labeled. Meaning no file can be uploaded until it's been labeled. Something to consider as well.

[#5]

Thanks for the replies Christian. But a key requirement is differentiating tenancies.

Eg allow a file to be uploaded to Teams tenant for an organisation but blocked for all other tenants

[#6]

Should be possible to scope that in a Defender for Cloud Apps session policy but can take a look at it later on.

@WillNunez So I've read the initial post again and understand the use case as you want to prevent uploading of files in third-party tenants. Can't say I have a good solution for this as those users already are members of that organization and adhere to their policies. I would probably use sensitivity labels as mentioned in the first reply or use tenant-restrictions, but for the latter you would break the collaboration and encryption part completely and the users will not be able to open the files. You certainly can prevent external sharing of files with DLP and use Defender for Cloud Apps with several settings controlling your own environment. But I just can't see what can be done here besides what has already been suggested.

Try with the official support and let us know if they have a solution. Thanks.

[#7]

@ChristianJBergstrom 

Lets think of a label "ForMyTenancyOnly"

Endpoint DLP can allow uploads to URLs with sharepoint.my-tenancy and my-sharepoint.my tenancy and block all others.

However how to a block/allow when using Teams (tenancy not in URL)? Or when using officeapps saving to Onedrive/sharepoint?

I was hoping CASB is the answer.

Office365 is API linked to Microsoft defender so I know i can write rules that would detect uploads to my tenancy.

The gap is how do i block that label from being uploaded to other domains/tenancy?

If I proxy all traffic through CASB (ie change proxy pacs so that all onedrive/sharepoint/teams) goes through CASB can defender policies differentiate between my domain/tenancy and any other

[#8 · Accepted solution]

Can’t see any way of preventing that ”gap” other than configuring permissions in the label/labels.

*edit @WillNunez just realized this should be possible by instead using Endpoint DLP policy.

https://learn.microsoft.com/en-us/microsoft-365/compliance/endpoint-dlp-using?view=o365-worldwide#sc...