Mission Least Privilege Function

Co-opting a secondary link as a covert data path succeeds where that link is absent from the mission's own picture of its flows. Maintaining the diagram is the governance answer.

The practice requires a current and accurate data-flow diagram covering mission essential flows including those passing through mission-external service providers, which is precisely the visibility a compromised partner site exploits the absence of. It is a discovery and inventory obligation, so it governs rather than interdicts. Note that this practice's title reads as least privilege while its description is data-flow mapping; the mapping follows the description.

A payload communication channel that routes host-bus data to customer networks is exactly the undocumented flow the diagram obligation exists to make visible.

Trusted relationships are the mission-external dependencies the data-flow diagram is required to cover. Knowing the flow is the precondition for governing the trust; the practice does not itself constrain it.

A vendor connection is a mission-external service provider flow the diagram must include, which is what makes an unexpected path through it visible.

The user segment is a mission-external flow in the same sense, and the diagram obligation is what surfaces its reach back into mission systems.