AI agents use opn_update_firewall_rule to create or update resources in OPNsense MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your OPNsense MCP Server environment.
Updating firewall rules is a reversible write operation that modifies network security policy. While impactful, it does not delete data (would be Destructive) or execute arbitrary code (would be Execute). However, severity is high because misconfigured firewall rules could disrupt critical network connectivity or inadvertently expose systems.
From the tool's definition Tool name 'opn_update_firewall_rule' indicates modification of firewall rules. Description is empty, but the name and context (managing OPNsense firewalls) clearly indicate this creates or modifies firewall rule data.
Documented attack patterns abuse exactly the kind of access opn_update_firewall_rule gives an agent:
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_firewall_rule:
{
"version": "1",
"default": "deny",
"tools": {
"opn_update_firewall_rule": {
"limits": [
{
"counter": "opn_update_firewall_rule_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}opn_update_firewall_rule 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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opn_update_firewall_rule. 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.
Register the OPNsense MCP Server MCP server in PolicyLayer and add a rule for opn_update_firewall_rule: 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.
opn_update_firewall_rule is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the opn_update_firewall_rule 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.
Set action: deny in the PolicyLayer policy for opn_update_firewall_rule. 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.
opn_update_firewall_rule 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.
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.
Free to start. No card required.
81 OPNsense MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.