pool_scrub

THE RISK

High Risk

Why pool_scrub needs a policy

This tool executes administrative operations on storage pools (start/stop/pause scrub), which are external operations whose effects depend on which pool is targeted and which action is chosen. While not destructive (scrubbing does not delete data), it is Execute because it triggers system processes with non-trivial side effects.

From the tool's definition Tool name 'pool_scrub' with description 'Start, stop, or pause a pool scrub' indicates execution of storage maintenance operations that trigger external system-level actions on ZFS pools.

Documented attack patterns abuse exactly the kind of access pool_scrub gives an agent:

POLICY

How to control pool_scrub

PolicyLayer is an MCP gateway — it sits between your AI agents and Truenas, and nothing reaches the server without passing your rules. This is the rule we recommend for pool_scrub:

policy.json

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

pool_scrub 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.

Create a free account and register Truenas — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

High-risk tools in Truenas → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about pool_scrub

What does the pool_scrub tool do? +

Start, stop, or pause a pool scrub. It is categorised as a Execute tool in the Truenas MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on pool_scrub? +

Register the Truenas MCP server in PolicyLayer and add a rule for pool_scrub: 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. Nothing to install.

What risk level is pool_scrub? +

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

Can I rate-limit pool_scrub? +

Yes. Add a rate_limit block to the pool_scrub 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 pool_scrub completely? +

Set action: deny in the PolicyLayer policy for pool_scrub. 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 pool_scrub? +

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

Enforce policy on every Truenas tool call.

Start from Truenas, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →