nfs_share_update

THE RISK

Medium Risk

Why nfs_share_update needs a policy

This tool modifies NFS share configurations, which is a reversible Write operation. However, severity is rated 'high' rather than 'medium' because misconfiguration of NFS shares can have significant blast radius: incorrect permissions could expose sensitive data, invalid configuration could disrupt network access for multiple systems, or overly permissive shares could create security vulnerabilities.

From the tool's definition Tool name 'nfs_share_update' and description 'Update an existing NFS share/export' indicate modification of existing configuration data.

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

POLICY

How to control nfs_share_update

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 nfs_share_update:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "nfs_share_update": {
      "limits": [
        {
          "counter": "nfs_share_update_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

nfs_share_update 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.

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.

LIMIT THIS TOOL →

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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.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about nfs_share_update

What does the nfs_share_update tool do? +

Update an existing NFS share/export. 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.

How do I enforce a policy on nfs_share_update? +

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

nfs_share_update is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit nfs_share_update? +

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

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

nfs_share_update 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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