chmod_items

THE RISK

Medium Risk

Why chmod_items needs a policy

chmod operations change access control metadata on files and directories. While this is a modification operation (Write category), it is reversible—permissions can be re-chmod'd to restore prior state. It does not delete data or move money, so it does not qualify as Destructive or Financial.

From the tool's definition Tool is named 'chmod_items' and described as 'Change permissions mode for multiple specified files/directories (POSIX-style).' This modifies file/directory metadata (permissions) reversibly.

Documented attack patterns abuse exactly the kind of access chmod_items gives an agent:

POLICY

How to control chmod_items

PolicyLayer is an MCP gateway — it sits between your AI agents and Filesystem, and nothing reaches the server without passing your rules. This is the rule we recommend for chmod_items:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "chmod_items": {
      "limits": [
        {
          "counter": "chmod_items_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

chmod_items 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.

Create a free account and register Filesystem — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Filesystem tools

Destructive delete_items Delete multiple specified files or directories. Execute chown_items Change owner (UID) and group (GID) for multiple specified files/directories. Write apply_diff Apply diffs to files Write copy_items Copy multiple specified files/directories. Write create_directories Create multiple specified directories (including intermediate ones). Write move_items Move or rename multiple specified files/directories. Write replace_content Replace content within files across multiple specified paths. Write write_content Write or append content to multiple specified files (creating directories if needed). NOTE

All 13 Filesystem tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about chmod_items

What does the chmod_items tool do? +

Change permissions mode for multiple specified files/directories (POSIX-style). It is categorised as a Write tool in the Filesystem MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on chmod_items? +

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

What risk level is chmod_items? +

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

Can I rate-limit chmod_items? +

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

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

chmod_items is provided by the Filesystem MCP server (sylphxai/filesystem-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Filesystem tool call.

Start from Filesystem, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →