pfsense_replace_system_tunables · Pfsense MCP: Risk & Policy

WHAT IT DOES

What pfsense_replace_system_tunables does on Pfsense

AI agents use pfsense_replace_system_tunables to create or update resources in Pfsense — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Pfsense environment.

WHY IT NEEDS A POLICY

Why pfsense_replace_system_tunables needs a policy

This tool modifies system tunable parameters on a firewall, which are reversible configuration changes but can have significant impact on firewall behavior, performance, and security posture. It's not destructive (data can be reverted), but affects critical system settings. The high severity reflects that misconfigured tunables could disable security features or degrade firewall functionality.

From the tool's definition PUT /api/v2/system/tunables - PUT HTTP method indicates modification of system tunables via REST API. Description indicates this replaces/modifies system configuration parameters on pfSense firewalls.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

pfsense_replace_system_tunables Rate-limited

pfsense_replace_system_tunables 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.

View as policy code

policy.json

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

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Pfsense, so you can run agents against it safely.

FAQ

Questions about pfsense_replace_system_tunables

What does the pfsense_replace_system_tunables tool do? +

PUT /api/v2/system/tunables. It is categorised as a Write tool in the Pfsense MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on pfsense_replace_system_tunables? +

Register the Pfsense MCP server in PolicyLayer and add a rule for pfsense_replace_system_tunables: 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 Pfsense. Nothing to install.

What risk level is pfsense_replace_system_tunables? +

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

Can I rate-limit pfsense_replace_system_tunables? +

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

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

pfsense_replace_system_tunables is provided by the Pfsense MCP server (abl030/pfsense-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.