opn_set_dnsbl

THE RISK

Medium Risk

Why opn_set_dnsbl needs a policy

The 'set' prefix indicates this tool modifies DNS blocklist configuration, which is a write operation that changes firewall security settings. While the description is empty (reducing confidence), the naming pattern and context within a firewall management server's security domain suggest the tool creates or modifies DNSBL rules.

From the tool's definition Tool name 'opn_set_dnsbl' indicates modification of DNS blocklist (DNSBL) settings. The 'set' verb denotes write operation. Sibling tools include 'opn_add_dnsbl_allowlist' which confirms this tool operates in DNS filtering domain.

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

POLICY

How to control opn_set_dnsbl

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_set_dnsbl:

policy.json

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

opn_set_dnsbl 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.

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.

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EXPLORE

Related tools and policies

More OPNsense MCP Server tools

Destructive opn_delete_alias opn_delete_alias Destructive opn_delete_ddns_account Delete a Dynamic DNS account by UUID and apply the configuration. Destructive opn_delete_dns_override opn_delete_dns_override Destructive opn_delete_dnsmasq_range Delete a dnsmasq DHCP range by UUID and apply the configuration. Destructive opn_delete_firewall_category opn_delete_firewall_category Destructive opn_delete_firewall_rule opn_delete_firewall_rule Destructive opn_delete_nat_rule opn_delete_nat_rule Destructive opn_haproxy_delete opn_haproxy_delete

All 81 OPNsense MCP Server tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about opn_set_dnsbl

What does the opn_set_dnsbl tool do? +

opn_set_dnsbl. 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.

How do I enforce a policy on opn_set_dnsbl? +

Register the OPNsense MCP Server MCP server in PolicyLayer and add a rule for opn_set_dnsbl: 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 opn_set_dnsbl? +

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

Can I rate-limit opn_set_dnsbl? +

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

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

opn_set_dnsbl 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.

Enforce policy on every OPNsense MCP Server tool call.

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.

CHECK YOUR STACK →