cmux_browser · Cmux MCP: Risk & Policy

WHAT IT DOES

What cmux_browser does on Cmux

AI agents invoke cmux_browser to trigger actions in Cmux. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why cmux_browser needs a policy

Browser control via an MCP agent involves executing arbitrary actions in a web browser, which can navigate to sites, interact with web applications, and trigger external operations. This is Execute-class because the effects depend on agent-supplied arguments and can include navigation, form submission, clicks, and other browser interactions.

From the tool's definition Tool name 'cmux_browser' and server description states it 'let agents control terminal panes, workspaces, input, and browser.' The description is incomplete ('Run a'), but the context indicates browser control capability.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

cmux_browser Rate-limited

cmux_browser stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "cmux_browser": {
      "limits": [
        {
          "counter": "cmux_browser_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Cmux, so you can run agents against it safely.

FAQ

Questions about cmux_browser

What does the cmux_browser tool do? +

Run a. It is categorised as a Execute tool in the Cmux MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on cmux_browser? +

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

What risk level is cmux_browser? +

cmux_browser is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit cmux_browser? +

Yes. Add a rate_limit block to the cmux_browser 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_browser completely? +

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

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