list_incoming_numbers

THE RISK

Low Risk

Why list_incoming_numbers needs a policy

This tool retrieves account phone number metadata without altering any data or triggering external operations. It is purely informational and carries minimal risk even if an AI agent lists all provisioned numbers. The blast radius is limited to information disclosure of phone number configuration details.

From the tool's definition Tool performs a listing/querying operation ('List Twilio-provisioned phone numbers') with filter options by PhoneNumber, FriendlyName, or Beta status. No modifications, deletions, or side effects are described.

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

POLICY

How to control list_incoming_numbers

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "list_incoming_numbers": {}
  }
}

list_incoming_numbers is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

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

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EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about list_incoming_numbers

What does the list_incoming_numbers tool do? +

List Twilio-provisioned phone numbers on this account. Filter by PhoneNumber (partial), FriendlyName, or Beta. It is categorised as a Read tool in the Mcp Afip MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on list_incoming_numbers? +

Register the Mcp Afip MCP server in PolicyLayer and add a rule for list_incoming_numbers: 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 Afip. Nothing to install.

What risk level is list_incoming_numbers? +

list_incoming_numbers is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit list_incoming_numbers? +

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

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

list_incoming_numbers is provided by the Mcp Afip MCP server (codespar/mcp-dev-latam). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Mcp Afip tool call.

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

CHECK YOUR STACK →