upload_attachment · Favro MCP: Risk & Policy

WHAT IT DOES

What upload_attachment does on Favro MCP

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

WHY IT NEEDS A POLICY

Why upload_attachment needs a policy

An AI agent can call upload_attachment faster than any human can review — one bad instruction and it creates or modifies resources in Favro MCP by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

upload_attachment Rate-limited

upload_attachment 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": {
    "upload_attachment": {
      "limits": [
        {
          "counter": "upload_attachment_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 Favro MCP, so you can run agents against it safely.

FAQ

Questions about upload_attachment

What does the upload_attachment tool do? +

Upload a file attachment to a card. It is categorised as a Write tool in the Favro 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 upload_attachment? +

Register the Favro MCP server in PolicyLayer and add a rule for upload_attachment: 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 Favro MCP. Nothing to install.

What risk level is upload_attachment? +

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

Can I rate-limit upload_attachment? +

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

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

upload_attachment is provided by the Favro MCP server (truls27a/favro-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.