Sentinelx Cloud Core MCP Server

sentinelx-cloud-core

The SentinelX agent. Install it on any Linux host and operate that host from Claude.ai or ChatGPT — allowlisted shell, structured file edits, and service management, over a single outbound WebSocket. No inbound ports.

Install (most people start here):

curl -fsSL https://get.sentinelx.app | sudo bash

This repo is also the agent's source — read on if you want to audit or contribute.

Architecture

                                        Internet
                                            │
   ┌────────────────┐                       │                  ┌─────────────────┐
   │  Claude.ai or  │   MCP over HTTPS      │   WebSocket      │  Your Linux box │
   │   ChatGPT      │ ◄───────────────────► │ ◄──────────────► │                 │
   │                │   (OAuth via Google)  │                  │  ┌───────────┐  │
   └────────────────┘                       │                  │  │  agent    │  │
                                ┌───────────────────────┐      │  │ (this)    │  │
                                │   mcp.sentinelx.app   │      │  └─────┬─────┘  │
                                │  (SentinelX hub —     │      │        │        │
                                │   closed source)      │      │   shell, edit,  │
                                └───────────────────────┘      │   service mgmt  │
                                                               └─────────────────┘

The agent is the box on the right. It opens one outbound WebSocket to the hub at install time (after enrollment) and stays connected. No inbound ports, no port-forwarding, no reverse tunnel.

What runs where

Supported platforms: any modern Linux distribution with systemd (tested on Ubuntu 22.04 / 24.04 and Debian 12). The agent also runs unmodified inside WSL2 on Windows — useful for developers who want SentinelX to manage their WSL environment alongside any other Linux hosts.

Tools exposed

The agent exposes its host's operations as MCP tools to your LLM via the hub:

sentinel_read, sentinel_list, and sentinel_search are read-only filesystem primitives. sentinel_edit and the mutating primitives (sentinel_move, sentinel_copy, sentinel_delete, sentinel_chmod, sentinel_chown) write. All of them give the LLM structured access to the filesystem without shelling out to cat/ls/mv/rm through exec, and all of them are gated by the same path allowlist (file_ops in the config, see below), not the command allowlist. Each path in that allowlist declares an access level: r (read-only ops) or rw (read-only ops plus the writing ops). Destructive operations that overwrite or remove an existing target make a timestamped backup first.

Config (/etc/sentinelx/config.yaml)

A starter config is generated at install time. Editable. Reloaded when the service restarts. Schema:

# Commands the agent can execute via the `exec` op. Prefix-matched against
# this list; empty/missing = nothing allowed (deny by default).
allowed_commands:
  - uptime
  - df -h
  - free
  - systemctl
  - sudo systemctl
  - journalctl
  # See config.example.yaml for the full starter list (file inspection,
  # networking, containers, git, etc.) plus opt-in categories
  # (Cloudflare tunnels, WireGuard, Android tooling, firewalling, SSH).

# Service units the agent is allowed to control via `service` / `restart`.
# Each unit explicitly lists which actions are permitted.
services:
  nginx:
    actions: [status, start, stop, restart, reload]
  docker:
    actions: [status, restart]
  # The agent itself, so the LLM can reload policy after editing the
  # config. Restarting re-reads /etc/sentinelx/config.yaml. Conservative
  # actions only — no start/stop, since the agent can't remotely start
  # itself once stopped.
  sentinelx-cloud-core:
    actions: [status, restart, is-active, is-enabled]
  # postgresql:
  #   actions: [status, start, stop, restart, reload]

# Optional: named playbooks the LLM can read or execute. Two shapes are
# supported and can coexist in the same map:
#
# 1) Diagnostic playbook — a fixed sequence of allowlisted commands the
#    agent can run in order. Useful for "give me a quick health snapshot"
#    type prompts where you want one named entry-point.
#
# 2) Procedure playbook — a structured recipe for the LLM to follow,
#    expressed in `description` / `when` / `steps` / `requires` / `notes`
#    fields. Pure documentation: the agent does NOT execute the steps,
#    the LLM reads them via `capabilities` and then calls the regular
#    tools (sentinel_exec, sentinel_edit, sentinel_service) on its own.
#
# See `config.example.yaml` for the full reference.
playbooks:
  # Diagnostic playbook (shape 1)
  health:
    description: "Show system health summary"
    commands:
      - "uptime"
      - "df -h /"
      - "free -m"

  # Procedure playbook (shape 2) — guides the LLM through extending the
  # allowlist itself. Useful so users can ask "let me run htop here" and
  # the LLM knows the exact procedure (edit config, restart service,
  # verify with capabilities).
  add_allowed_command:
    description: "How to add a new command to this host's allowlist"
    when: "User asks to allow a new command on this host"
    steps:
      - "Read /etc/sentinelx/config.yaml with sentinel_exec"
      - "Insert under allowed_commands with sentinel_edit (sudo, validator_preset=yaml)"
      - "Restart the agent: sentinel_service restart sentinelx-cloud-core"
      - "Verify with sentinel_capabilities"

# Logging
log:
  path: /var/log/sentinelx/core.log
  level: INFO

# SSRF defense for upload_file's file_url. The hostname must be in this
# allowlist AND must resolve to a public-routable IP (no loopback,
# RFC1918, link-local, etc.). Default empty = file_url disabled.
# Only add hosts YOU control — third-party hosts (github.com, pypi,
# random CDNs) expose your agent to supply-chain compromise.
security:
  trusted_fetch_hosts:
    - drop.pensa.ar
    - get.sentinelx.app
  file_url_timeout_seconds: 15

# Filesystem primitives (sentinel_read/list/search + edit, move, copy,
# delete, chmod, chown). Gated by a PATH allowlist, separate from the
# command allowlist above. Empty/missing = all the filesystem primitives
# are effectively disabled (they return path_not_allowed for any input).
#
# Each entry declares an access level:
#   r  = read-only ops (read, list, search) may touch this subtree
#   rw = read-only ops AND writing ops (edit, move, copy, delete,
#        chmod, chown) may touch this subtree
#
# A path is permitted only if, after canonicalization (symlinks
# resolved, .. collapsed), it falls under one of these entries. That
# canonical-resolve-then-prefix-check is what defeats both path
# traversal and symlink escapes. Writing ops additionally require the
# matched entry to be `rw`.
#
# Back-compat: an older `allowed_read_paths:` list is still accepted and
# is interpreted as a set of `r` entries (with a deprecation warning).
file_ops:
  paths:
    - path: /etc/nginx
      access: r
    - path: /var/log
      access: r
    - path: /home/youruser/projects
      access: rw
  max_read_bytes: 65536       # per read; larger files come back truncated
  max_list_entries: 1000      # per list
  max_search_results: 200     # per search

The agent only runs commands that prefix-match allowed_commands. So allowing git lets the LLM run git status, git log, etc.; allowing ls is enough to cover ls -lah /var/log. Out of the box the config is restrictive — see config.example.yaml for the full starter list with sensible categories.

There are two independent allowlists, and they protect different ops:

• allowed_commands gates exec (and the commands inside script_run).
• file_ops.paths gates every filesystem primitive — the read-only ones (sentinel_read, sentinel_list, sentinel_search) on any r or rw entry, and the writing ones (sentinel_edit, sentinel_move, sentinel_copy, sentinel_delete, sentinel_chmod, sentinel_chown) only on rw entries.

So a directory listed as r lets the LLM inspect it but not modify it; a directory listed as rw allows both. A directory in neither is invisible to all the filesystem primitives (the LLM would have to fall back to exec, which is governed by allowed_commands instead).

One deliberate exception: sentinel_edit with sudo=true is not gated by file_ops.paths. The trust boundary for sudo'd edits is the operator's sudoers policy, not the path allowlist — this is what lets the add_allowed_command playbook edit the root-owned config. Path canonicalization still runs (no traversal/symlink bypass); only the rw-membership check is waived for the sudo path. This carve-out and its residual risk are documented in THREAT_MODEL.md (§4.2.1).

Security model

• No inbound ports. Only an outbound WebSocket to the hub.
• JWT-bound identity. identity.json is signed by the hub at enrollment. Compromising one host doesn't grant access to others.
• Allowlist-gated. Anything not in config.yaml returns command_not_allowed. The agent won't synthesize new commands. This is the actual security boundary — not the unix user, not sudo policy. When a command is rejected, the agent returns a classified error (multi-line input, bash keyword, shell pipeline, or simply not in the allowlist) that points the LLM at the right tool instead of guessing.
• Path-allowlisted filesystem primitives. Every structured filesystem op only touches paths under file_ops.paths. Read-only ops (sentinel_read, sentinel_list, sentinel_search) work on r and rw entries; writing ops (sentinel_edit, sentinel_move, sentinel_copy, sentinel_delete, sentinel_chmod, sentinel_chown) require an rw entry. Paths are canonicalized — symlinks resolved, .. collapsed — before the prefix check, so neither path traversal nor a symlink pointing outside the allowlist can escape it. Empty allowlist = the primitives are disabled. Writing ops that overwrite or delete an existing target back it up first (timestamped .bak). sentinel_edit with sudo=true is a documented exception to the rw check — see THREAT_MODEL.md §4.2.1.
• Unprivileged user with passwordless sudo. The agent runs as sentinelx, not as root. By default the installer grants sentinelx passwordless sudo so it can manage services and edit system files — but it can still only invoke what's in your allowlist. To run with no sudo, set SENTINELX_SKIP_SUDO=1 during install.
• SSRF-defended file_url. When upload_file is called with a URL, the agent validates the hostname against security.trusted_fetch_hosts, resolves it to an IP, and rejects loopback / RFC1918 / link-local addresses (so an attacker can't pivot to cloud metadata services or LAN-internal hosts). Redirects are disabled, https only, default timeout 15s. The allowlist defaults to empty — file_url is effectively disabled until the operator opts into specific hosts.
• Path-traversal-defended uploads. All target_path arguments are resolved under upload_base via safe_path_under(); .. and absolute paths that escape are rejected up front.
• No telemetry. The agent reports nothing about your host or activity to anyone but the hub you're explicitly connected to.

For a deeper view, see THREAT_MODEL.md (assets, adversaries, trust boundaries, per-threat mitigations) and SECURITY.md (vulnerability reporting + disclosure policy).

Local development

git clone https://github.com/pensados/sentinelx-cloud-core
cd sentinelx-cloud-core
python3 -m venv .venv
source .venv/bin/activate
pip install -e '.[dev]'
pytest                              # unit tests

To run the agent against a hub other than the production one:

SENTINELX_HUB_URL=wss://localhost:8000/agent/connect \
  python3 -m sentinelx_core --identity-file /tmp/dev-identity.json

Vendored: pensa-safe-edit

The actual file mutation for sentinel_edit is done by a small stdlib-only module vendored at src/sentinelx_core/vendored/pensa_safe_edit.py. It is called in-process via its Python API (not shelled out), so there is no shell=True anywhere in the edit path. It does its work via temp files + atomic rename, makes a timestamped backup before mutating, preserves file metadata, and can run an optional pre-commit validator (json/yaml/toml/python/sh/nginx/systemd presets) — if validation fails the original file is left untouched. It is still also registered as a pip console-script entry point for standalone/manual use.

Related

• sentinelx-cloud-installer — the bash + python installer
• sentinelx-cloud-protocol — wire format spec

License

Apache License 2.0 — see LICENSE.