app_available

THE RISK

Low Risk

Why app_available needs a policy

This tool only reads and returns information about available applications; it performs no creation, modification, deletion, execution, or financial operations. The operation is purely informational with no side effects on the TrueNAS system.

From the tool's definition Tool name 'app_available' and description 'List all available apps from the catalog. Returns apps that can be installed.' indicate a query/list operation that retrieves catalog information without modifying state.

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

POLICY

How to control app_available

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_available:

policy.json

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

app_available 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

Related tools and policies

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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_available

What does the app_available tool do? +

List all available apps from the catalog. Returns apps that can be installed. 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_available? +

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

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

Can I rate-limit app_available? +

Yes. Add a rate_limit block to the app_available 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_available completely? +

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

app_available 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 →