opn_set_rule_categories

THE RISK

Medium Risk

Why opn_set_rule_categories needs a policy

This tool modifies firewall rule metadata (categories) rather than deleting rules or executing commands, placing it in Write category. Severity is high because misconfiguration of firewall rule categories could disrupt traffic filtering and security posture, though changes are reversible.

From the tool's definition Tool name 'opn_set_rule_categories' indicates modification of firewall rule categories on OPNsense. The 'set_' prefix denotes a write/modification operation. Description is empty, reducing certainty.

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

POLICY

How to control opn_set_rule_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_set_rule_categories:

policy.json

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

opn_set_rule_categories 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 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

Related tools and policies

More OPNsense MCP Server tools

Destructive opn_delete_alias opn_delete_alias Destructive opn_delete_ddns_account Delete a Dynamic DNS account by UUID and apply the configuration. Destructive opn_delete_dns_override opn_delete_dns_override Destructive opn_delete_dnsmasq_range Delete a dnsmasq DHCP range by UUID and apply the configuration. Destructive opn_delete_firewall_category opn_delete_firewall_category Destructive opn_delete_firewall_rule opn_delete_firewall_rule Destructive opn_delete_nat_rule opn_delete_nat_rule Destructive opn_haproxy_delete opn_haproxy_delete

All 81 OPNsense MCP Server tools →

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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 opn_set_rule_categories

What does the opn_set_rule_categories tool do? +

opn_set_rule_categories. It is categorised as a Write tool in the OPNsense MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on opn_set_rule_categories? +

Register the OPNsense MCP Server MCP server in PolicyLayer and add a rule for opn_set_rule_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_set_rule_categories? +

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

Can I rate-limit opn_set_rule_categories? +

Yes. Add a rate_limit block to the opn_set_rule_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_set_rule_categories completely? +

Set action: deny in the PolicyLayer policy for opn_set_rule_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_set_rule_categories? +

opn_set_rule_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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