curl_custom · Curl MCP Server MCP: Risk & Policy

WHAT IT DOES

What curl_custom does on Curl MCP Server

AI agents invoke curl_custom to trigger actions in Curl 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 curl_custom needs a policy

This tool allows execution of arbitrary curl commands determined by the user/agent. While curl itself is primarily a network utility, the ability to execute 'custom' commands with 'full control' means an agent could craft requests to exfiltrate data, interact with internal systems, or trigger unintended side effects on remote servers. The lack of apparent input constraints elevates this to Execute rather than Write.

From the tool's definition Tool description states 'Execute a custom curl command with full control' — the word 'Execute' combined with 'custom' and 'full control' indicates arbitrary command execution with user-supplied parameters.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

curl_custom Rate-limited

curl_custom 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": {
    "curl_custom": {
      "limits": [
        {
          "counter": "curl_custom_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 Curl MCP Server, so you can run agents against it safely.

FAQ

Questions about curl_custom

What does the curl_custom tool do? +

Execute a custom curl command with full control. It is categorised as a Execute tool in the Curl 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 curl_custom? +

Register the Curl MCP Server MCP server in PolicyLayer and add a rule for curl_custom: 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 Curl MCP Server. Nothing to install.

What risk level is curl_custom? +

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

Can I rate-limit curl_custom? +

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

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

curl_custom is provided by the Curl MCP Server MCP server (neeraj15022001/curl-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.