block_command

THE RISK

Medium Risk

Why block_command needs a policy

This tool creates or modifies configuration data (the command blacklist) in a reversible manner. While it affects system security controls, the change is not irreversible and does not execute code or delete data. The impact is primarily administrative configuration of the MCP server's own security policies rather than direct system harm, yielding medium severity.

From the tool's definition Tool description states it 'Add[s] a command to the blacklist' and modifies the blocked commands list. The sibling tool 'list_blocked_commands' confirms a persistent blacklist data structure being managed.

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

POLICY

How to control block_command

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "block_command": {
      "limits": [
        {
          "counter": "block_command_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

block_command stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

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

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Claude Desktop Commander MCP tools

Destructive force_terminate Force terminate a running terminal session. Destructive kill_process Terminate a running process by PID. Use with caution as this will Execute unblock_command Remove a command from the blacklist. Once unblocked, the command can be executed normally. Execute execute_command Execute a terminal command with timeout. Command will continue running in background if it Write create_directory Create a new directory or ensure a directory exists. Can create multiple Write edit_block Apply surgical text replacements to files. Best for small changes (<20% of file size). Write move_file Move or rename files and directories. Can move files between directories Write write_file Completely replace file contents. Best for large changes (>20% of file) or when edit_block

All 19 Claude Desktop Commander MCP tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about block_command

What does the block_command tool do? +

Add a command to the blacklist. Once blocked, the command cannot be executed until unblocked. It is categorised as a Write tool in the Claude Desktop Commander MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on block_command? +

Register the Claude Desktop Commander MCP server in PolicyLayer and add a rule for block_command: 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 Claude Desktop Commander MCP. Nothing to install.

What risk level is block_command? +

block_command is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit block_command? +

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

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

block_command is provided by the Claude Desktop Commander MCP server (strawhatai/claude-dev-tools). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Claude Desktop Commander MCP tool call.

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

CHECK YOUR STACK →