update_subscriber · Campaign Monitor MCP: Risk & Policy

WHAT IT DOES

What update_subscriber does on Campaign Monitor MCP

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

WHY IT NEEDS A POLICY

Why update_subscriber needs a policy

This tool creates or modifies subscriber data reversibly, fitting the Write category. While updates to subscriber information could impact email deliverability or campaign targeting if misused, the effects are not irreversible (data can be corrected) and no financial transactions are involved.

From the tool's definition Tool name 'update_subscriber' and description 'Update a subscriber' indicate modification of subscriber data. The Campaign Monitor API manages email campaigns and subscriber lists, making this a data modification operation without permanent deletion.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_subscriber Rate-limited

update_subscriber 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": {
    "update_subscriber": {
      "limits": [
        {
          "counter": "update_subscriber_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 Campaign Monitor MCP, so you can run agents against it safely.

FAQ

Questions about update_subscriber

What does the update_subscriber tool do? +

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

How do I enforce a policy on update_subscriber? +

Register the Campaign Monitor MCP server in PolicyLayer and add a rule for update_subscriber: 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 Campaign Monitor MCP. Nothing to install.

What risk level is update_subscriber? +

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

Can I rate-limit update_subscriber? +

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

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

update_subscriber is provided by the Campaign Monitor MCP server (pauliowest/cmon-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.