Microsoft Workplace Join Part 1: The Security Timebomb

By Chris Higgins, Technical Support Engineer, Bitglass

It’s no secret that enterprise users wish to access work data and applications from a mix of both corporate and personal devices. In order to help facilitate this mix of devices, Microsoft has introduced a new feature called Workplace Join into Azure Active Directory, Microsoft’s cloud-based directory and identity service. While the intent of streamlining user access to work-related data is helpful, the delivery of this feature has resulted in a large security gap—one that can’t easily be disabled. This is another example of an app vendor optimizing for user experience ahead of appropriate controls and protections—demonstrating the basis for the cloud app shared responsibility model and the need for third-party security solutions like cloud access security brokers (CASBs).

According to Microsoft, “...by using Workplace Join, information workers can join their personal devices with their company's workplace computers to access company resources and services. When you join your personal device to your workplace, it becomes a known device and provides seamless second factor authentication and Single Sign-On to workplace resources and applications.”

How does it work?

When a user links their Windows machine to "Access Work or School," the machine is registered in Azure AD, and a master OAuth token is created for use between all Microsoft client applications as well as Edge/I.E. browsers. Subsequent login attempts to any Office resource will cause the application to gather an access token and log in the user without ever prompting for credentials. The ideology behind this process is that logging in to Windows is enough to identify a user and give them unrestricted access to all Office 365 resources.

In plain language, this means that once you login to Office 365 from any device (Grandma’s PC, hotel kiosks, etc.), you, and anyone accessing that device, are logged in to Office 365 automatically moving forward.

Why is this such a big security issue?

Workplace Join undoes all of your organization’s hard work establishing strong identity processes and procedures—all so that an employee can access corporate data from Grandma’s PC (without entering credentials). Since Grandma only has three grandkids and one cat, it likely won’t take a sophisticated robot to guess her password—exposing corporate data to anyone who accesses her machine. Making matters worse, user accounts on Windows 10 don’t even require passwords, making it even easier for data to be exfiltrated from such unmanaged devices.

Workplace Join is enabled by default for all O365 tenants. Want to turn it off? You’ll have to wait for the next blog post to sort that out.

In the meantime, download the Definitive Guide to CASBs to learn how cloud access security brokers can help secure your sensitive data.