Tools / Microsoft Threat Modeling Tool (TMT) Interview questions
What is an external entity in TMT?
An external entity is anything that interacts with your system but sits outside the boundary you control and are modeling - a human user, a partner API, or another team's service you don't own.
Because you have no direct control over an external entity's internal behavior, TMT's rules focus its generated threats on Spoofing (can someone impersonate this actor?) and Repudiation (can this actor deny having sent something?), rather than Tampering or Elevation of Privilege, which apply to things inside your trust boundary that you're responsible for defending.
A common modeling mistake is drawing a service you actually own as an external entity just because it's a separate deployable - if you're responsible for its security posture, it usually belongs on the diagram as a process instead.
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