custom_upload_file · Marketo MCP Server MCP: Risk & Policy

WHAT IT DOES

What custom_upload_file does on Marketo MCP Server

AI agents use custom_upload_file to create or update resources in Marketo MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Marketo MCP Server environment.

WHY IT NEEDS A POLICY

Why custom_upload_file needs a policy

The name implies a file upload operation, which is a Write action. However, the empty description significantly lowers confidence. Given the Marketo context (marketing assets like emails, images), this likely uploads files to Marketo's file storage. Severity is high because an AI agent could upload malicious or unintended content at scale.

From the tool's definition Tool name 'custom_upload_file' suggests uploading/writing file data; description is empty and uninformative.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

custom_upload_file Rate-limited

custom_upload_file stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "custom_upload_file": {
      "limits": [
        {
          "counter": "custom_upload_file_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about custom_upload_file

What does the custom_upload_file tool do? +

custom_upload_file. It is categorised as a Write tool in the Marketo MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on custom_upload_file? +

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

What risk level is custom_upload_file? +

custom_upload_file is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit custom_upload_file? +

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

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

custom_upload_file is provided by the Marketo MCP Server MCP server (tyron-pretorius/marketo-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.