MCP policy enforcement

A tool-call policy check must bind the caller, task, tool name and arguments to an enforceable result.

01 / The operating case

What changes in a real workflow?

A gateway allows delete_file for a test folder; the server later receives the same call for a production folder through a direct connection.

Trace the authority boundary
  1. 01Client / task
  2. 02MCP server
  3. 03Tool call + arguments
  4. 04Downstream effect

02 / Decision contract

What the executor must check

Normalize and evaluate the requested path at the server or protected filesystem boundary, and ensure every route receives an equivalent check.

InputPrincipal · task · action · target
DecisionGrant ancestry · policy · current state
ResultEnforce · record · verify outcome

03 / Failure and evidence

What goes wrong, and what can be proven?

Failure mode

Policy exists in a gateway but the underlying executor accepts calls from another path.

Evidence to retain

Compare gateway decisions, server invocation IDs and filesystem changes to detect bypass.

04 / Canonical scope

Why this reference stands alone

Gateway security owns topology; this page owns the per-call enforcement contract.

Protocol or attack trace

Per-call binding

Sequence

Gateway allows delete_file(path=/test/a); server receives delete_file(path=/prod/a) through another connection.

Negative test

Executor denies changed path and any route with no matching decision digest.

Primary references

Read the underlying material

Architecture discussion

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