mcp-shell

mcp-shell

MCP server that runs shell commands. Your LLM gets a tool; you get control over what runs and how.

Built on mark3labs/mcp-go. Written in Go.

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Run it

Docker (easiest):

docker run -it --rm -v /tmp/mcp-workspace:/tmp/mcp-workspace sonirico/mcp-shell:latest

From source:

git clone https://github.com/sonirico/mcp-shell && cd mcp-shell
make install
mcp-shell

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Configure it

Secure mode is the default. With no config file, mcp-shell boots in secure mode and registers only typed tools: file reads, grep/glob, git inspection, and (opt-in) file/git writes and operator-defined scripts. There is no raw shell command. You only need a config file to change the defaults below. To run fully unrestricted you must opt in explicitly:

MCP_SHELL_ALLOW_UNSAFE=1 mcp-shell   # disables secure mode; the only tool is shell_exec

To customize the policy, point to a YAML config:

export MCP_SHELL_SEC_CONFIG_FILE=/path/to/security.yaml
mcp-shell

Secure mode (default) — typed tools only, every path confined to working_directory:

security:
  enabled: true
  working_directory: /tmp/mcp-workspace
  max_execution_time: 30s
  max_output_size: 1048576
  run_as_user: ""
  audit_log: true

  # Expose file and git write tools (write_file, edit_file, mkdir, move,
  # delete, git_add, git_commit, git_switch, git_restore, git_stash). Off by
  # default.
  writes_enabled: false

  # Operator-defined scripts exposed through the run_script tool. The client
  # picks a name; the argv is yours and cannot be altered.
  # scripts:
  #   test: ["go", "test", "./..."]
  #   lint: ["golangci-lint", "run"]

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Wire it up

Claude Desktop — add to your MCP config:

{
  "mcpServers": {
    "shell": {
      "command": "docker",
      "args": ["run", "--rm", "-i", "sonirico/mcp-shell:latest"],
      "env": { "MCP_SHELL_LOG_LEVEL": "info" }
    }
  }
}

For custom config, mount the file and set the env:

{
  "command": "docker",
  "args": ["run", "--rm", "-i", "-v", "/path/to/security.yaml:/etc/mcp-shell/security.yaml", "-e", "MCP_SHELL_SEC_CONFIG_FILE=/etc/mcp-shell/security.yaml", "sonirico/mcp-shell:latest"]
}

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Tools

Secure mode (the default) registers these typed tools. * marks a required parameter.

Every path parameter is resolved against working_directory (symlinks followed); anything outside it is rejected. Git paths and refs are passed positionally and validated: a ref starting with - is rejected. There are no network tools; push, fetch and clone are not offered.

Unrestricted mode: shell_exec exists only with MCP_SHELL_ALLOW_UNSAFE=1, runs the command through bash -c with no validation, by design, and it is the only tool registered in that mode.

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Environment variables

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Development

make install dev-tools   # deps + goimports, golines
make fmt test lint
make docker-build       # build image locally
make release            # binary + docker image

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Security

• Default: Secure mode. The server builds every command's argv itself; the client never supplies a shell string. Only typed tools are registered.
• Path confinement: every path parameter is resolved against working_directory, symlinks followed, and anything that resolves outside it is rejected.
• Git hardening: paths are passed after --, refs after --end-of-options, and a ref starting with - is rejected. Git runs with GIT_CONFIG_NOSYSTEM=1, GIT_CONFIG_GLOBAL=/dev/null, core.fsmonitor, core.pager and core.hooksPath neutralised, and --no-ext-diff --no-textconv on log/diff/show/blame.
• Minimal environment: child processes get only PATH, HOME and LANG, never the server's own environment or .env secrets.
• Writes and scripts are opt-in: writes_enabled: true exposes the file/git write tools; a non-empty scripts map exposes run_script. Both are off by default.
• Unrestricted: only via MCP_SHELL_ALLOW_UNSAFE=1. The only tool registered is shell_exec, which runs bash -c with no validation. Fine for local dev, dangerous otherwise.
• Docker: Runs as non-root, Alpine-based. Use it in production. Best paired with an OS sandbox (read-only FS, dropped caps) as defense-in-depth.

Threat model, guarantees, and the scope for vulnerability reports live in SECURITY.md. Read it before opening an advisory.

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Migrating from 0.x

Secure mode no longer validates a shell_exec command string; it exposes typed tools instead. A config file's security: block no longer accepts:

Loading a config file that still sets one of these fails at startup with an error naming the key. There is no more "legacy mode" and no security-legacy.yaml example. If you need raw shell access, set MCP_SHELL_ALLOW_UNSAFE=1 to get shell_exec back; it is no longer constrained by the security: block at all.

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Contributing

Fork, branch, make fmt test, open a PR.