Passive subdomain enumeration using Certificate Transparency logs
AI agents call subdomain_enum_passive to retrieve information from MCP Recon without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves subdomain information from publicly available Certificate Transparency logs. It is purely passive reconnaissance — no data is created, modified, deleted, or executed. The blast radius is minimal as it only aggregates publicly available information.
From the tool's definition Tool performs 'passive subdomain enumeration using Certificate Transparency logs' — a read-only information gathering activity that queries public certificate transparency data without modifying anything or triggering active network probes.
Documented attack patterns abuse exactly the kind of access subdomain_enum_passive gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Recon, and nothing reaches the server without passing your rules. This is the rule we recommend for subdomain_enum_passive:
{
"version": "1",
"default": "deny",
"tools": {
"subdomain_enum_passive": {}
}
}subdomain_enum_passive is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Passive subdomain enumeration using Certificate Transparency logs. It is categorised as a Read tool in the MCP Recon MCP Server, which means it retrieves data without modifying state.
Register the MCP Recon MCP server in PolicyLayer and add a rule for subdomain_enum_passive: 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 MCP Recon. Nothing to install.
subdomain_enum_passive is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the subdomain_enum_passive 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 subdomain_enum_passive. 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.
subdomain_enum_passive is provided by the MCP Recon MCP server (sundayz-hunter/mcp_recon). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from MCP Recon, 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.
13 MCP Recon tools catalogued and risk-classified — across an index of 43,000+ MCP servers.