upload_image · RendrKit MCP: Risk & Policy

WHAT IT DOES

What upload_image does on RendrKit

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

WHY IT NEEDS A POLICY

Why upload_image needs a policy

This tool creates and stores data (uploads images to a hosted service), making it a Write operation. Severity is medium because the blast radius is limited to storage/quota exhaustion and potential abuse of hosting resources, but the upload itself is reversible (images can be deleted). It does not execute arbitrary code, delete data, or move money.

From the tool's definition Tool description states 'Upload an image to get a hosted URL' — creates a new resource (hosted image) with side effects (storage allocation, URL generation). Accepts user-provided content (public URL or base64 data) and persists it.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

upload_image Rate-limited

upload_image 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_image": {
      "limits": [
        {
          "counter": "upload_image_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 RendrKit, so you can run agents against it safely.

FAQ

Questions about upload_image

What does the upload_image tool do? +

Upload an image to get a hosted URL that can be used as photo_url in templates. Provide either a public URL to re-upload or base64-encoded image data. It is categorised as a Write tool in the RendrKit 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_image? +

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

What risk level is upload_image? +

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

Can I rate-limit upload_image? +

Yes. Add a rate_limit block to the upload_image 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_image completely? +

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

upload_image is provided by the RendrKit MCP server (vbiff/rendrkit-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.