Microsoft’s Zero Trust guidance defines three core principles: “Verify explicitly, use least-privileged access, and assume breach.” In Microsoft’s SCI learning content and Zero Trust overview, the model is described as one that “treats every access attempt as though it originates from an open, untrusted network” and therefore requires explicit verification using all available signals (identity, device health, location, data sensitivity, and anomalies). This directly confirms the first statement as true: Verify explicitly is a guiding principle.

The same guidance states organizations must “assume breach”—designing controls so that if an attacker is already inside, blast radius is minimized through segmentation, Just-In-Time/Just-Enough-Access, continuous monitoring, and rapid detection and response. Microsoft’s Zero Trust materials repeatedly explain to “assume attackers are present” and to “contain and remediate” through defense-in-depth controls, which validates the second statement as true.

Finally, Zero Trust rejects perimeter-based implicit trust. Microsoft clarifies that the model does not rely on a trusted internal network protected by a firewall; instead it “never trusts, always verifies,” continuously enforcing policy regardless of network location (on-premises or internet). Therefore, the statement that Zero Trust assumes a firewall secures the internal network from external threats is false because Zero Trust presumes no inherent safety from being “inside” the network and requires continuous verification and least-privileged access everywhere.