MCP Design Risk Brief

The MCP flaw is a design decision. Contain it now.

The Model Context Protocol’s core design — tools described in natural language, invoked by a model that reads untrusted content — is not a bug that will be patched. It is a standing condition to be contained. Here is how.

The Standing Risks
01
Tool descriptions are instructions to the model.

A malicious or compromised server can steer agent behavior through its own tool metadata — no exploit required.

02
Untrusted content flows into trusted context.

Anything a tool returns — a web page, a ticket, an email — enters the same context window as your instructions.

03
Tool chaining creates unplanned capability.

Individually safe tools compose into unsafe sequences: read secret → encode → send. No single tool looks dangerous.

04
Sessions outlive the human’s attention.

Long-running agent sessions keep credentials and context alive long after the operator stopped watching.

The Containment Pattern
01
Mediate every tool call through a policy layer.

No direct model-to-tool path. Every invocation is classified, checked against policy, and logged before execution.

02
Quarantine untrusted tool output.

Wrap external content so the model treats it as data, never as instructions — and strip active instruction patterns.

03
Bound sessions in time and scope.

Sessions expire, credentials rotate, and idle agents lose authority automatically.

04
Detect dangerous chains, not just dangerous calls.

Evaluate sequences of tool calls against exfiltration and escalation patterns — the risk lives in the composition.

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