send_input

THE RISK

High Risk

Why send_input needs a policy

This tool interacts with live running processes by sending input to them, which can trigger arbitrary behavior depending on what the process is and what input is sent. Since it operates within Docker containers that execute shell commands, sending input could drive interactive shells, scripts, or other processes to perform significant actions.

From the tool's definition Send input to a running background process

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

POLICY

How to control send_input

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

policy.json

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

send_input 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.

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

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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All 9 Docker MCP Server tools →

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Go deeper

High-risk tools in Docker MCP Server → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-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.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about send_input

What does the send_input tool do? +

Send input to a running background process. It is categorised as a Execute tool in the Docker MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on send_input? +

Register the Docker MCP Server MCP server in PolicyLayer and add a rule for send_input: 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 Docker MCP Server. Nothing to install.

What risk level is send_input? +

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

Can I rate-limit send_input? +

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

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

send_input is provided by the Docker MCP Server MCP server (kenforthewin/docker-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Docker MCP Server tool call.

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

CHECK YOUR STACK →