Fix DMZ NAT issue - adds no-NAT rules for inter-VLAN traffic
AI agents use nat_fix_dmz to create or update resources in OPNSense MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your OPNSense MCP Server environment.
This tool creates new NAT rules (no-NAT rules) in the firewall configuration. While it modifies firewall/NAT rules which is significant, the action is 'adds' rules (Write/reversible) rather than deleting or overwriting existing ones. However, misconfiguration of NAT rules on a firewall could expose internal network segments or break security boundaries, making the blast radius high.
From the tool's definition Fix DMZ NAT issue - adds no-NAT rules for inter-VLAN traffic
Documented attack patterns abuse exactly the kind of access nat_fix_dmz 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 nat_fix_dmz:
{
"version": "1",
"default": "deny",
"tools": {
"nat_fix_dmz": {
"limits": [
{
"counter": "nat_fix_dmz_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}nat_fix_dmz 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.
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Fix DMZ NAT issue - adds no-NAT rules for inter-VLAN traffic. 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.
Register the OPNSense MCP Server MCP server in PolicyLayer and add a rule for nat_fix_dmz: 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.
nat_fix_dmz is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the nat_fix_dmz 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 nat_fix_dmz. 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.
nat_fix_dmz is provided by the OPNSense MCP Server MCP server (vespo92/opnsensemcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 196 OPNSense MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
196 OPNSense MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.