vm_display_uri

THE RISK

Low Risk

Why vm_display_uri needs a policy

This is a read-only operation that queries and returns connection information about an already-running virtual machine. The URI itself is not sensitive data—it's a standard connection string needed to access a VM console. Misuse would only allow an agent to connect to a VM console it shouldn't have access to, but that is a separate access control issue. The tool itself performs no side effects.

From the tool's definition Tool retrieves a display URI for an existing running VM ('Get the web display URI'). No data is modified, created, or deleted. The action is purely informational, returning connection details without affecting the VM or system state.

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

POLICY

How to control vm_display_uri

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 vm_display_uri:

policy.json

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

vm_display_uri 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 vm_display_uri

What does the vm_display_uri tool do? +

Get the web display URI (VNC/SPICE) for a running VM. Useful for connecting to the VM console. 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 vm_display_uri? +

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

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

Can I rate-limit vm_display_uri? +

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

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

vm_display_uri 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 →