run_smtp_user_enum

THE RISK

High Risk

Why run_smtp_user_enum needs a policy

This tool executes external reconnaissance operations (SMTP probing) whose effects depend on target arguments (server address, usernames to test). It is not merely reading cached data (Read), nor creating reversible artifacts (Write), nor destroying data (Destructive). It actively triggers network interactions and scans against remote systems, making it Execute category.

From the tool's definition Tool name 'run_smtp_user_enum' indicates execution of SMTP user enumeration, a reconnaissance technique that connects to SMTP servers and probes for valid usernames.

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

POLICY

How to control run_smtp_user_enum

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

policy.json

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

run_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.

Create a free account and register Pentester-MCP — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

Govern code and CI agents → Branch allowlists, approval on merges, and rate caps on the build and pipeline tools agents trigger.
High-risk tools in Pentester-MCP → 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 →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about run_smtp_user_enum

What does the run_smtp_user_enum tool do? +

run_smtp_user_enum. It is categorised as a Execute tool in the Pentester-MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on run_smtp_user_enum? +

Register the Pentester- MCP server in PolicyLayer and add a rule for run_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 Pentester-MCP. Nothing to install.

What risk level is run_smtp_user_enum? +

run_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 run_smtp_user_enum? +

Yes. Add a rate_limit block to the run_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 run_smtp_user_enum completely? +

Set action: deny in the PolicyLayer policy for run_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 run_smtp_user_enum? +

run_smtp_user_enum is provided by the Pentester- MCP server (halilkirazkaya/pentester-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Pentester-MCP tool call.

Start from Pentester-MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →