Create a new device and attach it to a VM. The
AI agents use vm_device_create to create or update resources in Truenas — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Truenas environment.
This tool creates a new VM device and attaches it to an existing virtual machine. While this modifies system configuration and VM state, it is reversible (the device can be detached and removed), so it falls into Write rather than Destructive.
From the tool's definition Tool name is 'vm_device_create' and description states 'Create a new device and attach it to a VM.' The verbs 'create' and 'attach' indicate data modification operations.
Documented attack patterns abuse exactly the kind of access vm_device_create gives an agent:
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_device_create:
{
"version": "1",
"default": "deny",
"tools": {
"vm_device_create": {
"limits": [
{
"counter": "vm_device_create_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}vm_device_create stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Create a new device and attach it to a VM. The. It is categorised as a Write tool in the Truenas MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Truenas MCP server in PolicyLayer and add a rule for vm_device_create: 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.
vm_device_create is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the vm_device_create 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.
Set action: deny in the PolicyLayer policy for vm_device_create. 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.
vm_device_create 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.
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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279 Truenas tools catalogued and risk-classified — across an index of 43,000+ MCP servers.