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Secure an MCP deployment by enforcing permissions outside the model, limiting each agent and server to the access its task requires, and treating tool results as untrusted input. Prompt instructions can guide behavior, but they cannot authorize a protected operation; logs can show what an agent did, but not necessarily why it did it.
Why does MCP security need more than a careful prompt?
An MCP integration lets an AI application retrieve information or invoke actions through connected servers. A resource or tool result may contain malicious instructions alongside legitimate data. If those instructions influence the agent’s next choice, the agent can make a technically authorized call that is nevertheless harmful in context.
Anthropic’s discussion of containment describes this audit blind spot: a record may show a successful, authorized API call after poisoned tool output steered an agent toward exfiltration. Google Cloud’s AI security guidance and the OWASP MCP Security Cheat Sheet also identify prompt injection, insecure tool chaining, and over-scoped access as risks.
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How should you limit what an agent can do?
Give each workload only the access its task needs
Use a distinct agent or workload identity where appropriate, and grant it only the roles and permissions needed for its assigned work. Prefer narrower token scopes when the underlying service supports them. Separate read-only work from write or administrative actions where possible, rather than giving every workflow the broadest access needed by any one of them.
Enforce authorization at the point of execution
Check access on the server or gateway before carrying out a protected operation. A tool description that says “read only,” or a prompt that tells the model not to write, is not a permission check. Apply authorization to the relevant server and, where available, to individual tools or protected operations. This helps prevent a compromised or misdirected agent from turning access to one function into permission to use another.
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Constrain local servers as well as remote access
For a locally run MCP server, restrict the process permissions and filesystem access to what it needs. The MCP Security Best Practices documentation calls out local process and filesystem restrictions; the project’s security overview also places responsibility on implementers to design servers with least privilege. Avoid running a local server with access to unrelated files or capabilities simply because they are available on the host.
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- Classify tool output as data, not authority. Do not let content retrieved through an MCP resource or tool override access rules or grant itself new permissions.
- Put a control point between results and model context where practical. A proxy can inspect or filter tool results before they reach the model. This creates an opportunity to catch suspicious content, but it cannot guarantee that every attack will be detected.
- Require deterministic checks for consequential actions. Enforce permissions independently of the model’s interpretation of the conversation. For high-impact operations, add a separate approval step when the deployment requires one.
- Review chains of actions, not only isolated calls. A sequence of individually permitted actions can have an unintended result. Consider whether the agent’s identity and policy allow the complete sequence, not just each tool in isolation.
These measures reduce exposure; they do not eliminate prompt injection. Do not make an agent’s ability to recognize an attack the sole safeguard against it.
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Which authorization approach fits your deployment?
Authorization design depends on who provisions access and where the check is enforced. User-approved per-server OAuth and organization-managed provisioning serve different administrative needs; neither replaces least privilege or server-side enforcement.
| Approach | How access is administered | What to verify |
|---|---|---|
| User-approved per-server OAuth | The user approves access for an individual server. | Confirm the granted scopes are no broader than the task requires, and that the server checks authorization before protected operations. |
| Enterprise-Managed Authorization (EMA) | Access can be provisioned centrally through an organization’s identity provider. | Check that the extension is supported by the clients and servers in your deployment, and that centrally provisioned access follows the organization’s policy. |
The MCP project announced the Enterprise-Managed Authorization extension as stable on June 18, 2026. Its availability in a particular deployment still depends on client and server support.
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Account for the authorization changes in the July 2026 specification
The MCP specification release dated July 28, 2026 includes issuer validation for authorization responses under RFC 9207, binds client credentials to the issuer that minted them, and formally deprecates Dynamic Client Registration (DCR) in favor of Client ID Metadata Documents (CIMD). If you target that revision, check the version-specific implementation and migration guidance for your SDKs and services; do not assume older integrations handle these changes automatically. The MCP roadmap published August 22, 2026 also discusses the status of authorization hardening and EMA.
What should MCP audit logs and telemetry capture?
Keep enough information to investigate an invocation and review whether policy was applied. OWASP’s invocation-logging guidance supports recording user context and timestamps. As an operational baseline, record:
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- the principal or workload identity that initiated the invocation;
- the server and tool or action requested;
- when the invocation occurred;
- the authorization or policy decision and whether execution proceeded.
Protect the records themselves: do not log access tokens or credentials, and avoid retaining sensitive payloads that are not needed for investigation. Choose retention and access controls appropriate to the sensitivity of the data and your organization’s requirements.
Logs have an important limit: an authorized-call record does not establish that the action was contextually intended, or reveal all the content that influenced the agent. Use logs to reconstruct identity, requested action, timing, and policy outcome—not as proof that the agent’s reasoning was safe.
Use the logging approach for your transport and protocol version
In the July 28, 2026 specification release, MCP’s Logging feature is deprecated. The release materials point to stderr for stdio transports and OpenTelemetry for structured observability. The May 21, 2026 release-candidate announcement says deprecated features remain supported for at least twelve months, but teams should plan against the lifecycle of the protocol version they actually use rather than building new observability around a deprecated feature.
Quick Recap
How can you put the controls into practice?
- Inventory the agent’s tasks and access. Identify the servers and operations each workflow needs, including whether it must read, write, or administer data.
- Narrow identities and permissions. Assign task-appropriate identities and scopes; separate read-only work from write or administrative work where the service permits it.
- Enforce policy before execution. Make the server or gateway verify authorization for each protected operation. Add an approval gate for high-impact actions where required.
- Constrain local execution. Limit local server process permissions and filesystem access to the task’s requirements.
- Handle tool results as untrusted. Consider proxy inspection before content enters model context, while recognizing that filtering is not a complete defense.
- Instrument and review invocations. Capture identity, requested action, time, and policy outcome through transport-appropriate logging and structured telemetry. Protect secrets and unnecessary sensitive data from exposure.
- Validate version and support. Check the target MCP revision, SDK behavior, and client/server support before adopting the July 2026 authorization changes or EMA.
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