set_firewall_rules · Hcloud MCP: Risk & Policy

WHAT IT DOES

What set_firewall_rules does on Hcloud

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

WHY IT NEEDS A POLICY

Why set_firewall_rules needs a policy

This tool modifies firewall rules on existing resources, which is a Write operation (creates or modifies data reversibly). While it overwrites existing rules, those rules can be reconfigured by subsequent calls, making it Write rather than Destructive.

From the tool's definition Tool description states it 'Set rules on an existing firewall (overwrites all rules)', indicating modification of existing firewall configuration data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_firewall_rules Rate-limited

set_firewall_rules 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": {
    "set_firewall_rules": {
      "limits": [
        {
          "counter": "set_firewall_rules_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 Hcloud, so you can run agents against it safely.

FAQ

Questions about set_firewall_rules

What does the set_firewall_rules tool do? +

Set rules on an existing firewall (overwrites all rules). Same rule format as create_firewall. It is categorised as a Write tool in the Hcloud MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_firewall_rules? +

Register the Hcloud MCP server in PolicyLayer and add a rule for set_firewall_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 Hcloud. Nothing to install.

What risk level is set_firewall_rules? +

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

Can I rate-limit set_firewall_rules? +

Yes. Add a rate_limit block to the set_firewall_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.

How do I block set_firewall_rules completely? +

Set action: deny in the PolicyLayer policy for set_firewall_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.

What MCP server provides set_firewall_rules? +

set_firewall_rules is provided by the Hcloud MCP server (xodus-co/hcloud-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.