Use review to reduce exposure, but do not rely on it as the last gate. For MCP and agent toolchains, runtime enforcement should be the decisive control because it governs the behaviour that emerges after installation. Review answers what a package looks like; runtime controls answer what it can do.
Where package review helps MCP security, and where it stops
Package review is useful for reducing obvious exposure before code or a tool is introduced, especially when you are trying to spot malicious dependencies, hidden install behaviour, or an unsafe distribution channel. It is a screening control, not a behavioural guarantee. For MCP, the central question is whether the package is trustworthy enough to consider, but the harder question is what the server, client, or agent will be allowed to do once it is running.
That distinction matters because MCP systems are not judged only by their contents at install time. They are judged by the actions they can take at runtime: which resources they can reach, which tokens they can present, which tools they can invoke, and whether they can exceed the intent of the operator or the user. A package can look clean and still become unsafe once connected to live credentials, live data, or a permissive agent workflow.
When teams treat review as the main gate, they often overestimate how much static inspection can tell them about a package that will execute inside a broader agentic environment. The safer pattern is to use review to filter out poor candidates, then use runtime policy to govern the package’s actual authority after deployment. That is the only way to control behaviour that emerges from configuration, context, and delegated access.
What runtime enforcement should decide in an MCP stack
runtime enforcement should decide whether the MCP component may proceed with a specific action at the moment it is requested. That includes request routing, tool invocation, token handling, outbound calls, and access to downstream systems. The decisive control is not the package’s declared intent, it is the live policy boundary that constrains what it can do in production.
For MCP, that usually means placing enforcement as close as possible to the execution point: gateway policy, server-side authorization, token audience restrictions, scoped credentials, and deny-by-default rules for tool use. The point is to make unsafe behaviour fail closed even if the package passed review, or if a benign package is later chained into a more dangerous workflow.
Review still matters, but it should answer a narrower question: is this package worth admitting into the trust boundary at all? Runtime controls answer the more important question: does this deployment have the authority to read, write, forward, or transform anything sensitive right now? In practice, the second question is the one that prevents real damage.
For a practical reference point on the protocol side, the Model Context Protocol: Authorization specification is useful because it frames MCP servers as authorization-aware components rather than passive libraries.
How to split responsibility between review and enforcement
Security teams get better results when they divide the work by control type. Review should focus on provenance, maintainer trust, dependency hygiene, and suspicious packaging patterns. Runtime enforcement should focus on authorization, isolation, session scope, and the consequences of a tool call that reaches beyond its original purpose. That split prevents the common mistake of asking code review to carry the burden of access control.
This is especially important for agent toolchains. Agents and MCP servers can compose actions dynamically, so the risk is not just what one package does in isolation, but what it can enable when connected to other tools and identities. If a package can only be used safely because runtime policy narrows its authority, then the runtime policy is the real control and should be designed, tested, and monitored accordingly.
A useful internal benchmark is the MCP Security Guide, which covers authorization, token passthrough, gateways, and the practical control points teams need to harden.
For package risk and dependency abuse patterns, the Malicious Package and Dependency Confusion Guide is a strong companion because it helps teams separate supply-chain vetting from the runtime question of whether a package should ever get meaningful authority.
When package review is enough to lower risk, and when it is not
Package review is usually enough to reject obviously bad software, reduce the chance of onboarding a known-bad dependency, and improve baseline hygiene. It becomes insufficient when the MCP component will operate with sensitive tokens, broad tool access, or a path to production systems. In those cases, the main risk is not installation, it is delegated execution.
If the package can touch secrets, invoke external tools, or mediate access to business systems, runtime enforcement must be the final arbiter. The more autonomous the workflow, the less you should trust static review to predict safe behaviour. That is why teams should assume that a reviewed package can still become dangerous if policy does not constrain its live permissions.
For teams building around agentic systems, the AI Agent Identity Security: The 2026 Deployment Guide helps frame why runtime authority and short-lived access matter more than packaging assurances alone.
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 and risk surface, while NIST SP 800-53 Rev 5 sets the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Agentic AI Top 10 | ASI03 — Identity & Privilege Abuse | MCP toolchains rely on delegated runtime authority that can be abused. |
| Recommendation — Constrain tool and privilege scope so agents cannot exceed approved authority. | ||
| OWASP API Security Top 10 | API5 — Broken Function Level Authorization | MCP runtime enforcement must block unauthorized function invocation paths. |
| Recommendation — Enforce function-level authorization on every MCP action at runtime. | ||
| NIST SP 800-53 Rev 5 | IA-5 — Authenticator Management | MCP enforcement depends on controlling token and credential lifecycle. |
| AC-6 — Least Privilege | The question centers on limiting what a running MCP package may do. | |
| Recommendation — Rotate and scope credentials so MCP components cannot reuse excessive access. Apply least privilege to every MCP tool, token, and downstream permission. | ||
Practitioner Guidance
What to prioritise: Treat package review as admission control and runtime enforcement as operational control. If you can only strengthen one, strengthen the policy that governs live tool use, credential scope, and downstream access.
What to verify: Confirm that the MCP component cannot gain broader access at runtime than the team intended during review. Test the actual tool path, not just the package contents, and verify that deny-by-default behaviour survives deployment changes.
Decision rule: If a reviewed package can influence production data, credentials, or external systems, do not rely on review alone. Require runtime authorization that can stop unsafe actions even when the package is already installed and active.
Practitioner takeaway: Review reduces uncertainty, but runtime enforcement reduces harm. For MCP, the control that constrains live behaviour is the one that should carry the real security decision.
Related resources from NHI Mgmt Group
Deepen Your Knowledge
Free weekly newsletter
Subscribe to the NHI & AI Identity Journal
The latest on NHI and Agentic AI security – articles, research, breaches, news and events every week.
Bonus 33% off our NHI Course when you subscribe.
Reviewed and updated by the NHIMG editorial team on October 23, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org