fill_memory · MCPEmulate MCP: Risk & Policy

WHAT IT DOES

What fill_memory does on MCPEmulate

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

WHY IT NEEDS A POLICY

Why fill_memory needs a policy

This tool creates or modifies memory state within an isolated emulator session (as indicated by the broader server context). While it changes data, it is reversible within the session and does not permanently delete data or move outside the emulator boundary. The impact is scoped to a single emulation session rather than system-wide, making it Write rather than Destructive or Execute.

From the tool's definition Tool description states it 'Fill[s] a memory range with a repeating byte pattern.' This directly modifies memory contents within an emulation session, which is a write operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fill_memory Rate-limited

fill_memory 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": {
    "fill_memory": {
      "limits": [
        {
          "counter": "fill_memory_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 MCPEmulate, so you can run agents against it safely.

FAQ

Questions about fill_memory

What does the fill_memory tool do? +

Fill a memory range with a repeating byte pattern. It is categorised as a Write tool in the MCPEmulate MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on fill_memory? +

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

What risk level is fill_memory? +

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

Can I rate-limit fill_memory? +

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

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

fill_memory is provided by the MCPEmulate MCP server (labguy94/mcpemulate). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.