opn_update_dns_override

THE RISK

Medium Risk

Why opn_update_dns_override needs a policy

This tool updates DNS overrides on an OPNsense firewall. DNS overrides control hostname-to-IP mappings, and unauthorized modifications could redirect traffic to malicious servers, poison DNS caches, or cause service disruptions. However, the action is reversible (records can be updated again), so it is Write rather than Destructive.

From the tool's definition Tool name 'opn_update_dns_override' indicates modification of DNS override settings. Sibling tools like 'opn_add_dns_override' and 'opn_add_dnsbl_allowlist' on a firewall management server confirm this operates in DNS configuration space.

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

POLICY

How to control opn_update_dns_override

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_update_dns_override:

policy.json

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

opn_update_dns_override 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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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

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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_update_dns_override

What does the opn_update_dns_override tool do? +

opn_update_dns_override. 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_update_dns_override? +

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

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

Can I rate-limit opn_update_dns_override? +

Yes. Add a rate_limit block to the opn_update_dns_override 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_update_dns_override completely? +

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

opn_update_dns_override 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.

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