opn_list_firewall_categories

THE RISK

Low Risk

Why opn_list_firewall_categories needs a policy

This tool queries and returns existing firewall rule categories without creating, modifying, deleting, or executing any operations. It is a pure read operation with minimal security impact; misuse would only expose non-sensitive categorization metadata.

From the tool's definition Tool name contains 'list' and description states 'List firewall rule categories' — a retrieval operation with no data modification or side effects.

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

POLICY

How to control opn_list_firewall_categories

PolicyLayer is an MCP gateway — it sits between your AI agents and OPNsense MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for opn_list_firewall_categories:

policy.json

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

opn_list_firewall_categories 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 OPNsense MCP Server — 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.
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FAQ

Questions about opn_list_firewall_categories

What does the opn_list_firewall_categories tool do? +

List firewall rule categories. It is categorised as a Read tool in the OPNsense MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on opn_list_firewall_categories? +

Register the OPNsense MCP Server MCP server in PolicyLayer and add a rule for opn_list_firewall_categories: 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 OPNsense MCP Server. Nothing to install.

What risk level is opn_list_firewall_categories? +

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

Can I rate-limit opn_list_firewall_categories? +

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

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

opn_list_firewall_categories is provided by the OPNsense MCP Server MCP server (lucamarien/opnsense-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every OPNsense MCP Server tool call.

Start from OPNsense MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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