extract_attachments · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What extract_attachments does on Nexus Core

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

WHY IT NEEDS A POLICY

Why extract_attachments needs a policy

The tool writes/saves files to the local filesystem. While it reads attachment data from a message, the primary action is persisting files to disk, making it a Write operation. Misuse could lead to writing unwanted or malicious files to allowed directories, hence medium severity.

From the tool's definition Save all attachments of a message into save_to_path (must be an existing dir inside ALLOWED_ROOTS)

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

extract_attachments Rate-limited

extract_attachments 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": {
    "extract_attachments": {
      "limits": [
        {
          "counter": "extract_attachments_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about extract_attachments

What does the extract_attachments tool do? +

Save all attachments of a message into save_to_path (must be an existing dir inside ALLOWED_ROOTS). It is categorised as a Write tool in the Nexus Core MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on extract_attachments? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for extract_attachments: 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 Nexus Core. Nothing to install.

What risk level is extract_attachments? +

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

Can I rate-limit extract_attachments? +

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

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

extract_attachments is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.