filesystem_get_acl

THE RISK

Low Risk

Why filesystem_get_acl needs a policy

This tool queries and returns ACL information for a filesystem path without modifying, deleting, or executing any operations. It is a pure read operation with minimal blast radius — an AI agent could misuse it to enumerate permissions but cannot directly escalate privileges, modify data, or execute commands through this tool alone. Low severity is appropriate for informational reads.

From the tool's definition Tool description explicitly states 'Get the Access Control List (ACL)' — a retrieval operation with no modification or side effects. The word 'Get' and the read-only nature of querying ACL permissions confirms this is a data retrieval action.

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

POLICY

How to control filesystem_get_acl

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 filesystem_get_acl:

policy.json

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

filesystem_get_acl 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.

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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 filesystem_get_acl

What does the filesystem_get_acl tool do? +

Get the Access Control List (ACL) for a file or directory path. Optionally return a simplified representation. 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 filesystem_get_acl? +

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

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

Can I rate-limit filesystem_get_acl? +

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

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

filesystem_get_acl 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.

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