app_categories

THE RISK

Low Risk

Why app_categories needs a policy

This tool retrieves and lists application categories from a catalog. It is a read-only query operation that does not modify, create, delete, or execute any code. The action is informational only, making it low severity with minimal blast radius if misused by an agent.

From the tool's definition Tool name 'app_categories' combined with description 'List all app categories available in the catalog' indicates a retrieval operation with no side effects.

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

POLICY

How to control app_categories

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 app_categories:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "app_categories": {}
  }
}

app_categories is read-only, so it stays allowed — but 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.

CAP THIS TOOL →

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EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about app_categories

What does the app_categories tool do? +

List all app categories available in the catalog. It is categorised as a Read tool in the Truenas MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on app_categories? +

Register the Truenas MCP server in PolicyLayer and add a rule for app_categories: 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 app_categories? +

app_categories is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit app_categories? +

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

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

app_categories 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 →