enumerate_subdomains | PolicyLayer

WHAT IT DOES

What enumerate_subdomains does on External Reconnaissance MCP Server

AI agents invoke enumerate_subdomains to trigger actions in External Reconnaissance MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

THE RISK

High Risk

Why enumerate_subdomains needs a policy

This tool triggers external network operations (subdomain enumeration via dnsrecon) whose effects and scope depend on the target domain argument supplied by the caller. It is not a passive read (Read) because it actively probes and interacts with external systems. It does not persist or irreversibly modify data (not Destructive or Write).

From the tool's definition Tool executes an external reconnaissance command (dnsrecon tool) that performs subdomain enumeration. The description explicitly states it 'Enumerate[s] subdomains using dnsrecon tool' — dnsrecon is an active reconnaissance tool that executes DNS queries and…

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

POLICY

How to control enumerate_subdomains

PolicyLayer is an MCP gateway — it sits between your AI agents and External Reconnaissance MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for enumerate_subdomains:

policy.json

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

enumerate_subdomains 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 External Reconnaissance MCP Server — nothing to install.
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Point your MCP client (Claude, Cursor, anything) at your gateway URL.

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EXPLORE

Related tools and policies

More External Reconnaissance MCP Server tools

Execute bruteforce_subdomains Bruteforce subdomains using dnsrecon and custom wordlist. Execute attempt_zone_transfer Attempt to perform a DNS zone transfer (AXFR) to enumerate all DNS records. Read enumerate_dns_records Enumerate various DNS record types for the target domain. Read run_dig_lookup perform simple lookup of any A records for the domain. Read run_whois_lookup perform query of domain ownership details. Read analyze_http_headers Analyze HTTP headers of the target domain. Read check_email_security Check email security configuration

All 8 External Reconnaissance MCP Server tools →

Execute tools on other servers

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Go deeper

High-risk tools in External Reconnaissance 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.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about enumerate_subdomains

What does the enumerate_subdomains tool do? +

Enumerate subdomains using dnsrecon tool. It is categorised as a Execute tool in the External Reconnaissance 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 enumerate_subdomains? +

Register the External Reconnaissance MCP Server MCP server in PolicyLayer and add a rule for enumerate_subdomains: 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 External Reconnaissance MCP Server. Nothing to install.

What risk level is enumerate_subdomains? +

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

Can I rate-limit enumerate_subdomains? +

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

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

enumerate_subdomains is provided by the External Reconnaissance MCP Server MCP server (naebo/mcp-external-recon-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every External Reconnaissance MCP Server tool call.

Start from External Reconnaissance 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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8 External Reconnaissance MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.