cmux_close_window

THE RISK

Critical Risk

Why cmux_close_window needs a policy

Closing a window in a terminal multiplexer like tmux/cmux permanently destroys the window and all associated panes and running processes. This cannot be undone — any unsaved work or running sessions are lost. This qualifies as Destructive due to the irreversible nature of the action. Severity is high because it can terminate multiple parallel AI CLI sessions and browser instances at once.

From the tool's definition 'Close a window' — closing a window is an irreversible action that terminates the window and any sessions/panes running within it, destroying their state.

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

POLICY

How to control cmux_close_window

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

policy.json

{
  "version": "1",
  "default": "deny",
  "hide": [
    "cmux_close_window"
  ]
}

cmux_close_window disappears from the agent's tool list entirely, and any attempt to call it is denied. The rest of the server keeps working.

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

RESTRICT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Cmux Agent tools

Destructive cmux_clear_notifications Clear all notifications. Destructive cmux_close_all Close ALL workspaces (or all except specific ones). Use Destructive cmux_close_surface Close a surface (tab). Destructive cmux_close_workspace Close one or more workspaces and all their panes. Pass a single ref or an array of refs. Execute cmux_browser_console Get or clear browser console logs/errors. Execute cmux_batch Execute multiple CMUX operations in a single MCP call. Each step references an existing cm Execute cmux_browser_eval Execute JavaScript in the browser page. Execute cmux_browser_navigate Navigate the browser: goto a URL, or go back/forward/reload.

All 63 Cmux Agent tools →

Destructive tools on other servers

Android Forensics ADB MCP Server create_full_backup 0xarchive web3_revoke_key Frida Game Hacking MCP clear_scan cPanel MCP Server clear_spam_box

Go deeper

Critical-risk tools in Cmux Agent → Every critical-risk tool this server exposes, in one view.
All critical-risk MCP tools → Every critical-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Blast radius → How much damage one compromised or confused agent can do — and how to bound it.
Tool call approval → Approval gates on individual tool calls: auto-allow, prompt, or deny.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about cmux_close_window

What does the cmux_close_window tool do? +

Close a window. It is categorised as a Destructive tool in the Cmux Agent MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.

How do I enforce a policy on cmux_close_window? +

Register the Cmux Agent MCP server in PolicyLayer and add a rule for cmux_close_window: 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 Cmux Agent. Nothing to install.

What risk level is cmux_close_window? +

cmux_close_window is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.

Can I rate-limit cmux_close_window? +

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

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

cmux_close_window is provided by the Cmux Agent MCP server (multiagentcognition/cmux-agent-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Cmux Agent tool call.

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

CHECK YOUR STACK →