cmux_close_surface

THE RISK

Critical Risk

Why cmux_close_surface needs a policy

Closing a surface/tab is an irreversible action that terminates a running session or workspace. Any unsaved state, running processes, or ongoing work within that tab would be lost. This constitutes an irreversible destruction of the surface and its associated state, warranting a Destructive classification with high severity given the potential blast radius of terminating active AI CLI sessions or browser instances.

From the tool's definition Close a surface (tab)

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

POLICY

How to control cmux_close_surface

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_surface:

policy.json

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

cmux_close_surface 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_window Close a window. 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_surface

What does the cmux_close_surface tool do? +

Close a surface (tab). 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_surface? +

Register the Cmux Agent MCP server in PolicyLayer and add a rule for cmux_close_surface: 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_surface? +

cmux_close_surface 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_surface? +

Yes. Add a rate_limit block to the cmux_close_surface 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_surface completely? +

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

cmux_close_surface 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 →