file_share · M365 MCP: Risk & Policy

WHAT IT DOES

What file_share does on M365

AI agents use file_share to create or update resources in M365 — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your M365 environment.

WHY IT NEEDS A POLICY

Why file_share needs a policy

File sharing operations modify access control metadata and sharing configurations, making them Write operations. The high severity reflects that an AI agent misusing this tool could broadly expose sensitive documents across an organization.

From the tool's definition Tool named 'file_share' on a Microsoft 365 server that manages OneDrive and file services. The name 'file_share' indicates sharing/modifying access controls on files, which is a write operation that changes data state (permissions/sharing settings).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

file_share Rate-limited

file_share 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": {
    "file_share": {
      "limits": [
        {
          "counter": "file_share_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 M365, so you can run agents against it safely.

FAQ

Questions about file_share

What does the file_share tool do? +

file_share. It is categorised as a Write tool in the M365 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on file_share? +

Register the M365 MCP server in PolicyLayer and add a rule for file_share: 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 M365. Nothing to install.

What risk level is file_share? +

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

Can I rate-limit file_share? +

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

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

file_share is provided by the M365 MCP server (robin-collins/m365-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.