host_exec · Ns Hpc MCP: Risk & Policy

WHAT IT DOES

What host_exec does on Ns Hpc

AI agents invoke host_exec to trigger actions in Ns Hpc. 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.

WHY IT NEEDS A POLICY

Why host_exec needs a policy

host_exec executes commands on the host system, making it Execute category. Severity is high because even 'pre-configured' commands can have broad effects in an HPC environment (resource consumption, data access, system state changes), though the sandboxing and pre-configuration constraints mitigate it from critical.

From the tool's definition Tool description states it can 'Run a pre-configured host command', which executes external operations. The server description emphasizes 'sandboxed interface' and 'bubblewrap isolation', indicating awareness that execution capabilities pose risks requiring…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

host_exec Rate-limited

host_exec 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "host_exec": {
      "limits": [
        {
          "counter": "host_exec_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Ns Hpc, so you can run agents against it safely.

FAQ

Questions about host_exec

What does the host_exec tool do? +

Run a pre-configured host command or list available commands. It is categorised as a Execute tool in the Ns Hpc MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on host_exec? +

Register the Ns Hpc MCP server in PolicyLayer and add a rule for host_exec: 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 Ns Hpc. Nothing to install.

What risk level is host_exec? +

host_exec is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit host_exec? +

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

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

host_exec is provided by the Ns Hpc MCP server (li-yq/namespaced-hpc-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.