Run two negative tests: give the agent a scope the user does not have, and give the user a scope the agent does not have. Both calls should fail. If either direction succeeds, the system is not enforcing intersection, and you have found a privilege expansion path rather than a least-privilege control.
How to prove the agent is not widening privilege
The fastest way to test least privilege is to make the authorization boundary fail in both directions. If the agent can act on a scope the user lacks, or if the user can induce the agent to act on a scope the agent lacks, you are not testing a mere permission check, you are testing whether the system truly enforces the intersection of authorities.
A good test case should be written around a real business action, not a toy read-only query. Use the same path the production agent would use, then vary only the authority boundary. That reveals whether policy is enforced at decision time, at tool execution time, or only in the user interface.
When the test passes, the agent should be unable to expand access, impersonate a broader principal, or reuse a more privileged token than the user intended. When it fails, the problem is usually not the model itself, it is the delegation design around the model, the tool gateway, or the downstream service that accepts the call.
Where least privilege breaks in agentic systems
Most failures come from one of three places: the agent is given its own broad standing access, the user context is not actually carried into downstream authorization, or the system merges user and agent privileges too early. That last case is the dangerous one, because it can look correct in logs while silently authorizing more than either party should have alone.
Teams should also check whether the agent can switch identities, cache a privileged token, or chain a benign permission into a broader action. A system can appear constrained on the first hop and still fail the moment the agent asks a tool, API, or workflow engine to perform the real action on its behalf.
For agents that touch cloud or identity-heavy workflows, the boundary between “user may request” and “agent may execute” needs explicit design. NHIMG’s IAM and IGA Basics is a useful reference point for thinking about how authorization, entitlement, and governance fit together before you trust an agent with production actions.
How to structure a meaningful negative test
Start by picking one operation that matters, then define two authority sets, one for the user and one for the agent. Your first negative test should prove the agent cannot exceed the user’s scope. Your second should prove the user cannot ask the agent to exercise capabilities the agent does not independently hold. If both directions do not fail cleanly, the control is not enforcing least privilege.
Run the same test against the exact tool, API, or backend that the agent will use in production, not just the chat layer. If the test only fails in the UI, the system still has a privilege expansion path. If it fails at the policy layer but succeeds through a direct service call, you have a bypass in the integration surface.
Where agent authorization is already a design goal, use a reference model that separates user intent from agent capability. NHIMG’s AI Agent Authorisation Guide and Authorisation Models Guide both help when you need to validate whether the policy decision is actually based on intersecting authority rather than a loosely scoped runtime token.
Risk and Threat Considerations
Least privilege failures in agents are high impact because they turn a narrow request channel into an action amplifier. A compromised prompt, a confused deputy pattern, or a mis-scoped token can let the agent perform actions that neither the user nor the agent should have been able to perform alone.
Failure mechanism: The system authorizes the user and the agent independently, then executes the broader of the two, or it passes a token that preserves excess privilege across tool calls. That creates a privilege expansion path even when the initial request looks normal.
Impact: The agent can reach data, administrative functions, or destructive operations outside the intended blast radius, which increases the chance of unauthorized access, data exposure, and irreversible operational damage.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Agentic AI Top 10 and OWASP Non-Human Identity Top 10 address the attack and risk surface, while NIST SP 800-53 Rev 5, NIST Zero Trust (SP 800-207) and OWASP ASVS set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | IA-2 — Identification and Authentication (Organizational Users) | Agents must be tied to the user who is invoking them. |
| IA-9 — Service Identification and Authentication | Agent-to-tool calls depend on service authentication and bounded delegation. | |
| AC-6 — Least Privilege | The question is explicitly about proving least privilege enforcement. | |
| Recommendation — Validate that the agent's actions remain bound to the authenticated user context. Enforce service authentication so the agent cannot exceed approved tool authority. Test that each action is allowed only at the minimum authority required. | ||
| NIST Zero Trust (SP 800-207) | Least privilege access | Zero Trust requires explicit least privilege at every request boundary. |
| Recommendation — Apply least-privilege checks at each agent and tool access decision. | ||
| OWASP Agentic AI Top 10 | ASI03 — Identity & Privilege Abuse | A failed intersection check is a privilege-abuse condition in agentic systems. |
| Recommendation — Test that the agent cannot inherit or expand privilege beyond the intended boundary. | ||
| OWASP Non-Human Identity Top 10 | NHI-05 — Overprivileged NHI | The test detects whether the agent can act with excess privilege. |
| NHI-10 — Human Use of NHI | The user must not be able to drive the agent beyond its own authority. | |
| Recommendation — Verify that non-human actors cannot perform actions outside their assigned scope. Block user-driven requests that would make the agent act outside its own privileges. | ||
| OWASP ASVS | V8 — Authorization | The core test is whether authorization is enforced at the action boundary. |
| Recommendation — Verify that authorization decisions are enforced before privileged actions execute. | ||
Practitioner Guidance
What to verify: Prove that the decision point evaluates both identities, the requesting user and the acting agent, at the point of use. You want evidence that a denied scope is denied even when the other side of the interaction would permit it.
Common mistake: Teams often test only whether the agent obeys the user, or only whether the user can invoke the agent. That misses the intersection rule and leaves open the exact expansion path that negative testing is meant to catch.
Practitioner takeaway: Treat a passing least-privilege test as evidence that neither principal can widen the other’s authority, not as proof that the agent is merely “restricted enough.”
Related resources from NHI Mgmt Group
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Reviewed and updated by the NHIMG editorial team on October 22, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org