smtp_user_enum · Kali Linux Security Tools MCP Server MCP

WHAT IT DOES

What smtp_user_enum does on Kali Linux Security Tools MCP Server

AI agents invoke smtp_user_enum to trigger actions in Kali Linux Security Tools 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.

WHY IT NEEDS A POLICY

Why smtp_user_enum needs a policy

This tool actively probes SMTP servers using protocol commands (VRFY, EXPN, RCPT) to enumerate valid user accounts. It triggers external network operations against mail servers, making it Execute category. Severity is high because it can be used for reconnaissance to harvest valid email/user accounts on target mail servers, enabling follow-on attacks like credential stuffing or phishing.

From the tool's definition Enumerate SMTP users. Modes: VRFY, EXPN, RCPT. WARNING: Only test authorized mail servers.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

smtp_user_enum Rate-limited

smtp_user_enum 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.

View as policy code

policy.json

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

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Kali Linux Security Tools MCP Server, so you can run agents against it safely.

FAQ

Questions about smtp_user_enum

What does the smtp_user_enum tool do? +

Enumerate SMTP users. Modes: VRFY, EXPN, RCPT. WARNING: Only test authorized mail servers. It is categorised as a Execute tool in the Kali Linux Security Tools 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 smtp_user_enum? +

Register the Kali Linux Security Tools MCP Server MCP server in PolicyLayer and add a rule for smtp_user_enum: 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 Kali Linux Security Tools MCP Server. Nothing to install.

What risk level is smtp_user_enum? +

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

Can I rate-limit smtp_user_enum? +

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

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

smtp_user_enum is provided by the Kali Linux Security Tools MCP Server MCP server (jesseeikeland/kali-linux-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.