Use governance controls to define who and what is allowed, then use runtime blocking to stop misuse once a session starts. If a control cannot see the prompt, the response content, and the action sequence together, it is not enough for active attack containment.
Why this decision is really about control timing, not control type
MCP teams should treat governance controls as the policy layer and runtime blocking as the containment layer. Governance decides which clients, tools, scopes, and deployment patterns are acceptable before use; runtime blocking intervenes when the session state, prompt content, or tool sequence shows misuse in progress. That split matters because a static approval process cannot see everything an active interaction can.
For MCP, the practical question is whether the control is meant to prevent bad configuration or stop bad behaviour once an agent is already operating. Governance is strongest when you need durable rules for registration, tool exposure, token handling, and approval boundaries. Runtime blocking is strongest when the risk depends on what the model is actually asking for, returning, or chaining during the session.
MCP Security Guide is useful here because it separates authorization design from abuse paths such as tool poisoning and token passthrough, which are different problems from simple access approval.
What runtime blocking can see that governance cannot
Runtime blocking becomes necessary when the abuse is only visible in context: the prompt may look legitimate in isolation, but the tool request, response content, and action sequence together reveal a harmful path. That is why blocking should be considered when the control decision depends on sequence, chain length, destination, or response content rather than on a static allow or deny rule.
In practice, this is the point where teams need a control that can evaluate the whole interaction, not just the identity of the caller. If the session begins to pivot from normal retrieval into unauthorized exfiltration, unsafe tool chaining, or unexpected command execution, the correct control is to interrupt the action path rather than wait for a later review cycle.
Model Context Protocol: Authorization specification is relevant because it shows the protocol boundary for authorization, while runtime blocking handles the downstream behaviour that protocol approval alone cannot judge.
AI Agent Identity Security: The 2026 Deployment Guide helps teams think about short-lived authority and task-scoped access, which are useful complements to session-time blocking when agent behaviour can change after initial approval.
How to draw the line between governance and blocking without overcontrolling MCP
Use governance controls for stable decisions that should not depend on runtime content: who may register an MCP server, which tools can be exposed, which environments may be reached, and which credential patterns are acceptable. Use runtime blocking when the question is not “was this approved?” but “is this interaction now becoming unsafe?”
The cleanest rule is to ask whether the control can still do its job if the session has already started changing shape. If the answer is no, governance alone is too weak. If the answer is yes, but only because you are willing to stop the session when content or action flow crosses a boundary, then runtime blocking is the right companion control.
OWASP Agentic Applications Top 10 is a useful reference because it frames agent goal hijack, tool misuse, and identity or privilege abuse as runtime risks, not just onboarding risks.
OWASP Agentic AI Top 10 reinforces the same point from a broader practitioner angle: runtime misuse has to be contained where the abuse happens, not only where the system is initially approved.
Risk and Threat Considerations
The main risk is assuming that pre-approval can contain active misuse. In MCP-style environments, an attacker or malfunctioning agent may stay within an apparently allowed session while steering requests toward unintended tools, overbroad responses, or chained actions that governance checks will not see in time.
Failure mechanism: Governance evaluates static permission boundaries, but it does not observe the live prompt, response, and action sequence together. That creates a blind spot for tool poisoning, prompt-driven abuse, and session-level privilege expansion unless runtime blocking is available.
Impact: A session can remain formally “allowed” while still causing data exposure, unsafe tool execution, or lateral movement through trusted integrations. The result is delayed containment, wider blast radius, and weaker evidence of what the agent actually did.
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 API Security Top 10 address the attack surface, NIST SP 800-53 Rev 5 sets the technical controls, and ISO/IEC 27001:2022 defines the regulatory obligations.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Agentic AI Top 10 | ASI02 — Tool Misuse | MCP tool abuse is a live agent risk that needs runtime containment. |
| ASI03 — Identity & Privilege Abuse | MCP decisions hinge on delegated authority and overbroad runtime access. | |
| Recommendation — Block unsafe tool calls once session behaviour turns abusive. Constrain agent authority to the minimum task-scoped privilege. | ||
| OWASP API Security Top 10 | API8 — Security Misconfiguration | MCP governance is about preventing insecure exposure and misconfigured access paths. |
| Recommendation — Harden exposed MCP endpoints and validate access configuration before release. | ||
| NIST SP 800-53 Rev 5 | AC-3 — Access Enforcement | Governance controls define who and what is allowed to use MCP resources. |
| AU-2 — Event Logging | Runtime blocking depends on visibility into prompt, response, and action sequence. | |
| SI-4 — System Monitoring | Active attack containment for MCP requires monitoring for unsafe behaviour as it happens. | |
| Recommendation — Enforce policy decisions before requests reach sensitive tools or data. Log session activity needed to detect and stop misuse in progress. Monitor live interactions and interrupt suspicious tool-use patterns immediately. | ||
| ISO/IEC 27001:2022 | A.8.5 — Secure authentication | MCP access decisions depend on strong authentication for clients and sessions. |
| A.8.16 — Monitoring activities | Runtime blocking needs monitoring that can observe and react to live session misuse. | |
| Recommendation — Require strong authentication before any MCP session can start. Monitor MCP sessions for unsafe sequences and terminate them when needed. | ||
Practitioner Guidance
What to verify: Confirm that governance rules define the allowed surface, then test whether a runtime control can still inspect the live interaction and stop the session on behavioural signals. If it cannot see prompt, response, and action flow together, treat it as approval logic, not containment.
Decision rule: If the control is about who may start or configure MCP use, keep it in governance. If the control must interrupt misuse after execution begins, require runtime blocking with clear stop conditions and logging for the blocked action path.
Practitioner takeaway: MCP needs both layers, but they solve different problems, governance limits what may begin, runtime blocking limits what may continue once the interaction turns unsafe.
Related resources from NHI Mgmt Group
- How should teams decide between schema governance and runtime blocking for GraphQL risk?
- What is the difference between human IAM controls and NHI governance?
- How should security teams decide between native ERP controls and a separate governance platform?
- How should security teams decide between posture, exposure, and runtime controls?