stop_vm · Truenas Ws MCP: Risk & Policy

WHAT IT DOES

What stop_vm does on Truenas Ws

AI agents invoke stop_vm to trigger actions in Truenas Ws. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why stop_vm needs a policy

This tool executes a command to stop a running VM, which is a real-time system operation affecting infrastructure state. It is not merely reading data (Read), nor is it creating/modifying configuration persistently (Write in the reversible sense), nor is it permanently destroying data (Destructive).

From the tool's definition Tool performs 'Stop a virtual machine' with graceful shutdown followed by forced termination—an active operation that triggers external system changes with side effects that depend on which VM is targeted.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

stop_vm Rate-limited

stop_vm stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "stop_vm": {
      "limits": [
        {
          "counter": "stop_vm_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Truenas Ws, so you can run agents against it safely.

FAQ

Questions about stop_vm

What does the stop_vm tool do? +

Stop a virtual machine. Attempts graceful shutdown first, forces after timeout. It is categorised as a Execute tool in the Truenas Ws MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on stop_vm? +

Register the Truenas Ws MCP server in PolicyLayer and add a rule for stop_vm: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Truenas Ws. Nothing to install.

What risk level is stop_vm? +

stop_vm is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit stop_vm? +

Yes. Add a rate_limit block to the stop_vm rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block stop_vm completely? +

Set action: deny in the PolicyLayer policy for stop_vm. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides stop_vm? +

stop_vm is provided by the Truenas Ws MCP server (thoriphes/truenas-ws-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.