AI agents invoke app_stop to trigger actions in Truenas. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool executes an operation to halt a running application, which qualifies as Execute rather than Write. The blast radius is high because stopping critical apps could cause service outages, data loss in flight, or cascading failures in a TrueNAS infrastructure. The tool accepts an app ID argument, making the effect dependent on what application the AI targets.
From the tool's definition Tool description: 'Stop a running app by its ID.' The action 'stop' on a running application is an external operation that triggers state changes on the TrueNAS system.
Documented attack patterns abuse exactly the kind of access app_stop 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 app_stop:
{
"version": "1",
"default": "deny",
"tools": {
"app_stop": {
"limits": [
{
"counter": "app_stop_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}app_stop stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
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Stop a running app by its ID. It is categorised as a Execute tool in the Truenas MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Truenas MCP server in PolicyLayer and add a rule for app_stop: 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.
app_stop is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the app_stop 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 app_stop. 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.
app_stop 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.