Take a screenshot of the CMUX window using macOS screencapture.
AI agents call cmux_screenshot to retrieve information from Cmux Agent without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves visual data from the screen without side effects. It does not create, modify, delete, or execute any operations. The action is purely observational and reversible with zero blast radius. While screenshots could theoretically expose sensitive information on screen, the tool itself performs only a read operation.
From the tool's definition Takes a screenshot of the CMUX window using macOS screencapture - captures visual output with no modification, deletion, or code execution capabilities.
Documented attack patterns abuse exactly the kind of access cmux_screenshot gives an agent:
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_screenshot:
{
"version": "1",
"default": "deny",
"tools": {
"cmux_screenshot": {}
}
}cmux_screenshot is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Take a screenshot of the CMUX window using macOS screencapture. It is categorised as a Read tool in the Cmux Agent MCP Server, which means it retrieves data without modifying state.
Register the Cmux Agent MCP server in PolicyLayer and add a rule for cmux_screenshot: 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.
cmux_screenshot is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the cmux_screenshot 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.
Set action: deny in the PolicyLayer policy for cmux_screenshot. 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.
cmux_screenshot 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.
Start from Cmux Agent, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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63 Cmux Agent tools catalogued and risk-classified — across an index of 43,000+ MCP servers.