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Microsoft 365 Office 365

Critical Office 365 External Sharing Security Gotcha

In an Office 365 Tenant, you must be careful with External Sharing in a few different scenarios:

1) If your organization has migrated from an existing on premise Farm in which you used “NT AuthorityAuthenticated Users” to grant permissions

2) If your organization is making use of External sharing via “Everyone” (including external users) in Office 365

If your organization’s Office 365 Admin has allowed External Sharing for Authenticated Users:


And has also enabled External Sharing on 1 or more External Site Collections:


If a Site user shares anything (a document, folder, library, site etc.) with an external user:


That user become part your Organization’s Office 365 Tenant Directory.

Once part of this Directory, Any Site Collection that is configured for External Sharing and has permissions granted to securables via “NT AuthorityAuthenticated Users” or “Everyone” will now be available to all External Users (as well as organization users) with whom anyone at your company has shared anything with


Be extremely careful to review your permissions before opening up external sharing!

Andrew Sutton

About Andrew Sutton

Andrew Sutton, “Drew”, is an Practice Director at Netwoven. Drew has 10+ years of experience working across a breadth of technologies and business verticals and is a Business Technologist at heart. Drew is tenured in overseeing and executing successful offshore projects and has been an integral player in defining the Global Delivery Strategy at Netwoven.

He has architected and delivered solutions for Organizational Portals, Extranets, Document and Records Management, Enterprise Information Architectures and Taxonomies, Enterprise Search, Cloud 3Cs, Virtualized Server Infrastructure with SAN Storage and large scale homogenous and heterogeneous Migrations, amongst others. Drew’s unique combination of business acumen, technical know-how and ability to quickly immerse into new areas have proven integral to the success of numerous projects.


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