AI agents call opn_list_nat_rules to retrieve information from OPNsense MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves or displays existing NAT rules from the OPNsense firewall—a read-only query operation. While the description is empty, the naming convention strongly indicates a read-only function. NAT rules are configuration data, and listing them presents low blast radius: viewing firewall configuration is informational only and has no destructive or operational side effects.
From the tool's definition Tool name 'opn_list_nat_rules' contains 'list', indicating data retrieval. The verb 'list' is explicitly a Read operation that queries existing NAT rules without modification.
Documented attack patterns abuse exactly the kind of access opn_list_nat_rules gives an agent:
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_nat_rules:
{
"version": "1",
"default": "deny",
"tools": {
"opn_list_nat_rules": {}
}
}opn_list_nat_rules is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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opn_list_nat_rules. It is categorised as a Read tool in the OPNsense MCP Server MCP Server, which means it retrieves data without modifying state.
Register the OPNsense MCP Server MCP server in PolicyLayer and add a rule for opn_list_nat_rules: 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.
opn_list_nat_rules is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the opn_list_nat_rules 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 opn_list_nat_rules. 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.
opn_list_nat_rules 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.
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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81 OPNsense MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.