Boundary testing is the practice of checking whether a system can go beyond its permitted scope or perform actions it was not authorized to do. In cyber security, it is used to validate limits such as role-based access, API permissions, workflow constraints, data boundaries, and stop conditions. The goal is to prove that a tool, service, or AI agent cannot escape its assigned rules even when inputs are unusual, malformed, or intentionally manipulative.
This matters because many attacks try to cross trust boundaries: a low-privilege user attempts a privileged action, an automated agent is pushed to call the wrong tool, or a workflow continues after it should have stopped. Boundary tests help defenders find weak authorization checks, missing guardrails, and unsafe integrations before an attacker does. Good boundary testing produces evidence that controls are enforced at runtime, not just documented on paper.