acme_sign_certificate

THE RISK

High Risk

Signing/issuing a certificate triggers an external cryptographic operation and interacts with ACME certificate authorities. This is not a simple write (it invokes external processes and protocols), and it can have significant security implications if misused—e.g., issuing certificates for unintended domains. It falls under Execute due to triggering external operations whose effects depend on arguments.

From the tool's definition Issue/sign a certificate (initial creation or re-issue)

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

HOW TO CONTROL ACME_SIGN_CERTIFICATE

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 acme_sign_certificate:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "acme_sign_certificate": {
      "limits": [
        {
          "counter": "acme_sign_certificate_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

acme_sign_certificate stays usable, but rate-capped — a runaway agent can't fire it dozens of times 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.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

More OPNSense MCP Server tools

Destructive acme_delete_action Delete an ACME automation action Destructive acme_revoke_certificate Revoke a certificate Destructive cert_delete Delete a certificate Destructive delete_firewall_rule Delete a firewall rule Destructive delete_vlan Delete a VLAN Destructive firewall_delete_rule Delete a firewall rule Destructive haproxy_acl_delete Delete an HAProxy ACL Destructive haproxy_action_delete Delete an HAProxy action

All 196 OPNSense MCP Server tools →

Execute tools on other servers

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Go deeper

High-risk tools in OPNSense MCP Server → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

What does the acme_sign_certificate tool do? +

Issue/sign a certificate (initial creation or re-issue). It is categorised as a Execute tool in the OPNSense MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on acme_sign_certificate? +

Register the OPNSense MCP Server MCP server in PolicyLayer and add a rule for acme_sign_certificate: 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 acme_sign_certificate? +

acme_sign_certificate is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit acme_sign_certificate? +

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

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

acme_sign_certificate 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.

Enforce policy on every OPNSense MCP Server tool call.

Deterministic rules across all 196 OPNSense MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.

GOVERN OPNSENSE →

Free to start. No card required.

196 OPNSense MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.

// WHAT ACME_SIGN_CERTIFICATE ON OPNSENSE MCP SERVER DOES

// THE RISK

// HOW TO CONTROL ACME_SIGN_CERTIFICATE

// EXPLORE