store.blob-put · MCP: Risk & Policy

WHAT IT DOES

What store.blob-put does on Mcp

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

WHY IT NEEDS A POLICY

Why store.blob-put needs a policy

This tool creates or modifies data (uploads files) but does not irreversibly delete data, so it is Write rather than Destructive. However, severity is high because combined with the financial aspect (pay-per-call in USDC), misuse could result in substantial unintended charges if an agent triggers multiple large uploads.

From the tool's definition Tool uploads or creates a file via a 'paid call' operation. The description explicitly states 'upload a file (any bytes)' which is a write operation that creates new data in persistent storage.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

store.blob-put Rate-limited

store.blob-put 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": {
    "store.blob-put": {
      "limits": [
        {
          "counter": "store.blob-put_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 Mcp, so you can run agents against it safely.

FAQ

Questions about store.blob-put

What does the store.blob-put tool do? +

STORE: upload a file (any bytes) in a single paid call. It is categorised as a Write tool in the 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 store.blob-put? +

Register the MCP server in PolicyLayer and add a rule for store.blob-put: 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 Mcp. Nothing to install.

What risk level is store.blob-put? +

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

Can I rate-limit store.blob-put? +

Yes. Add a rate_limit block to the store.blob-put 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 store.blob-put completely? +

Set action: deny in the PolicyLayer policy for store.blob-put. 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 store.blob-put? +

store.blob-put is provided by the MCP server (@2sio/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.