SSH MCP Server v2

SSH MCP Server is a security-first Model Context Protocol server that gives LLM agents controlled SSH access to remote hosts — with command classification, policy-based authorization, human-in-the-loop approval, and full audit logging.

The risk this server exists to manage. Giving an LLM shell access on a remote host puts private data, untrusted input and network egress in one place — Simon Willison's "lethal trifecta". Prompt injection has no general fix, so ssh-mcp assumes any command may be attacker-influenced: it classifies before executing, authorizes against a role × host-group matrix, gates destructive work behind approval, and records the decision either way. That narrows the blast radius; it does not remove the risk. Two things stay yours: never point it at a root account, and **never set auto approval on a production profile**. SECURITY.md has the full threat model.

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Quick Start

1. Install

npm install -g ssh-mcp

2. Configure

Create ~/.config/ssh-mcp/config.toml (Linux/macOS) or %APPDATA%\ssh-mcp\config.toml (Windows):

[defaults]
defaultProfile = "dev"
approvalMode = "ask-destructive"

[[profiles]]
name = "dev"
host = "192.168.1.100"
port = 22
user = "deploy"           # NOT root!
auth = "key"
keyRef = "~/.ssh/id_ed25519"
role = "admin"
approvalPolicy = "auto"    # dev is permissive

chmod 600 ~/.config/ssh-mcp/config.toml

3. Set credentials via environment variables

export SSH_MCP_PASSWORD="your-password"        # if using auth=password
# OR use SSH agent (recommended):
export SSH_AUTH_SOCK="$SSH_AUTH_SOCK"           # already set if agent running

4. Connect from your MCP client

Claude Code:

claude mcp add --transport stdio ssh-mcp -- ssh-mcp

Claude Desktop / Cursor / Windsurf:

{
  "mcpServers": {
    "ssh-mcp": {
      "command": "ssh-mcp",
      "env": {
        "SSH_MCP_PASSWORD": "your-password"
      }
    }
  }
}

Never pass passwords as CLI arguments — they're visible via ps aux. Use env vars, config files, SSH agent, or OS keychain.

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Tools (11)

Interactive Sessions

Sessions maintain state (CWD, environment variables) between commands:

Agent: open-session(name="deploy", type="interactive")
Agent: run-command(session="deploy", command="cd /opt/myapp")
Agent: run-command(session="deploy", command="git pull")    # runs in /opt/myapp
Agent: run-command(session="deploy", command="npm ci")      # CWD persists
Agent: close-session(name="deploy")

Background Sessions

Long-running processes (logs, builds):

Agent: open-session(name="logs", type="background", command="tail -f /var/log/syslog")
Agent: read-session-output(name="logs", lines=20)   # poll
Agent: close-session(name="logs")

Remote host support

Tested against Linux (Debian/bash, Alpine/busybox ash), Dropbear, and Windows

OpenSSH on Windows 11.

Interactive sessions require a POSIX shell (sh, bash, ash, zsh). They work by

bracketing each command with printf markers and reading $? and $PWD from a

trailer — none of which exist in cmd.exe, the default shell for Windows

OpenSSH. Opening one against such a host fails immediately with an explicit

error rather than timing out; everything else works normally.

Setting PowerShell as the OpenSSH DefaultShell does not help: the protocol is

POSIX-specific, not merely non-cmd.

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Configuration

Profile options

[defaults]
defaultProfile = "dev"
sessionMaxPerConnection = 5
sessionIdleTimeoutMs = 600000       # 10min
sessionBackgroundMaxMs = 3600000    # 1hr
commandTimeoutMs = 60000
commandMaxChars = 5000              # 0 = unlimited, the config spelling of --maxChars=none
commandMaxOutputBytes = 1048576     # 1MB
connectionIdleReapMs = 900000       # 15min
commandQuotaPerDay = 0              # 0 = unlimited; circuit breaker for runaway agents
approvalGrantTtlMs = 0              # 0 = always prompt; see "Approval Grants"
approvalMode = "ask-destructive"    # auto | ask-destructive | ask-all | deny

[[profiles]]
name = "prod-web-1"
host = "10.0.1.50"
port = 22
user = "deploy"
auth = "agent"                      # agent | key | password | keychain
keyRef = "~/.ssh/id_ed25519"        # for auth=key
keychainEntry = "ssh-mcp/prod"      # for auth=keychain (requires @napi-rs/keyring)
via = "bastion"                     # ProxyJump — route through bastion profile
group = "prod"                      # Policy tier: prod | staging | dev, or your own (see [policy])
workdir = "/var/www"
trustedHostKey = "SHA256:..."       # Pin host key (optional)
tty = false
role = "operator"                   # viewer | operator | admin
readOnly = false
approvalPolicy = "ask-all"
cert = false                        # SSH CA cert auth — auto-detects keyRef-cert.pub
sessionMaxPerConnection = 3         # per-profile override
sessionIdleTimeoutMs = 300000       # stricter for prod
commandQuotaPerDay = 200            # per-profile override
maxChars = 2000                     # per-profile override; stricter for prod

# Optional. Merged over the built-in role matrix; see "Policy Engine" below.
# roleBindings is keyed by role and then by tier, so the block below changes
# operator on prod and leaves operator's other tiers, and viewer and admin,
# on their defaults.
[policy]
denylist = ["^terraform\\s+destroy"]

[policy.roleBindings.operator]
prod = ["read-only", "safe", "destructive"]

Unknown sections and keys are a startup error, not a warning, so a typo cannot

leave you running defaults you thought you had overridden. That extends to role

and tier names: every one you write under [policy.roleBindings] has to be

reachable by some profile, and every profile's role and tier has to resolve to

real bindings. Both directions are checked at startup.

ProxyJump (Bastion)

Reach internal hosts behind a bastion/jump server. The via field specifies a profile name to tunnel through:

[[profiles]]
name = "bastion"
host = "bastion.example.com"
user = "deploy"
auth = "agent"

[[profiles]]
name = "internal-db"
host = "10.0.1.50"                 # private IP — not directly reachable
user = "dbadmin"
auth = "key"
keyRef = "~/.ssh/db_key"
via = "bastion"                     # tunnel through bastion

No agent forwarding — only a TCP tunnel via forwardOut. The bastion stays connected and reusable for multiple internal hosts.

SSH CA Certificates

For enterprise setups with a central SSH Certificate Authority:

[[profiles]]
name = "prod-db"
host = "db.internal"
user = "admin"
auth = "key"
keyRef = "~/.ssh/id_ed25519"
cert = true                         # enable CA cert auth

The certificate file is auto-detected using OpenSSH convention (keyRef + -cert.pub, e.g. ~/.ssh/id_ed25519-cert.pub). You can override the path with SSH_MCP__CERT env var. The cert is concatenated with the private key per ssh2 convention.

Credential Resolution Order

1. SSH agent (SSH_AUTH_SOCK) — no key material in process memory

2. OS keychain (macOS Keychain / Windows Credential Manager / Linux Secret Service) — requires auth = "keychain" and @napi-rs/keyring

3. Environment variables — SSH_MCP_PASSWORD, SSH_MCP_KEY, SSH_MCP_SUDO_PASSWORD, or profile-specific SSH_MCP__PASSWORD

4. Key file — keyRef path or SSH_MCP_KEY env var

Never CLI arguments. v2 removes --password, --sudoPassword, --suPassword entirely.

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Policy Engine

Roles

Which column applies comes from the profile's group. Set it explicitly —

without it the tier is guessed from the profile name (prod/staging/dev,

local, test, sandbox), and **an unrecognised name resolves to prod**,

the strictest tier. A production host named web-01 is therefore treated as

production rather than silently getting dev permissions.

Note what this means for sudo: **admin has no privileged on prod**, so

privileged-command is refused there by design — including on a quick-start

profile, which has no name to infer from and therefore lands on prod. If the

host is not production, say so:

npx ssh-mcp --host=10.0.0.5 --user=deploy --group=dev

[[profiles]]
name = "build-box"
group = "dev"

Configuring the matrix

The table above is the default, not a limit. An optional [policy] section is

merged over it at startup, so granting sudo on a host you have honestly

labelled prod is a reviewable line in a config file rather than a relabelling:

[policy.roleBindings.admin]
prod = ["read-only", "safe", "destructive", "privileged"]

The merge is at role *and* tier depth. That block changes admin on prod and

nothing else: admin on staging and dev keep their defaults, and viewer

and operator are untouched. Roles and tiers the defaults have never heard of

are added rather than rejected, which is what makes a custom group resolve to

real bindings instead of falling back to the strictest tier:

[[profiles]]
name = "build-box"
role = "admin"
group = "tier-1"

[policy.roleBindings.admin]
"tier-1" = ["read-only", "safe", "destructive"]

Extra deny patterns live in the same section, and are applied on top of the

never-allowed list rather than replacing it:

[policy]
denylist = ["^terraform\\s+destroy"]

Because role and tier names are free strings, nothing in the merge itself can

tell a new custom role from a misspelling of an existing one. A cross-check at

startup does, and these all fail there rather than at the point of use:

• a command class outside read-only | safe | destructive | privileged, so a

priviledged typo cannot parse into a grant of nothing and then read as a

policy decision when a command is refused;

• any unrecognised section or key anywhere in the config, so a block the parser

does not understand is an error rather than a clean startup with none of the

behaviour you configured;

• a role or tier under [policy.roleBindings] that no profile uses, so

[policy.roleBindings.operater] cannot merge in as a fourth role while the

profiles you meant to restrict keep running on defaults;

• a profile whose role has no bindings, or whose tier has none under that

role, so a host cannot end up on read-only for a reason nobody wrote down.

The last one covers the tier you did not set as well as the one you did. A

profile with no group still resolves to one by name, and that inferred tier

has to exist under the profile's role like any other.

A tier with no bindings for a role grants read-only, and never another tier's

classes. There is no fallback between tiers: while the matrix was compiled in,

falling back to prod meant falling back to a role's strictest cell, but a

[policy] block can write that cell now.

An OPA sidecar is not an alternative route to the same grant. OPA is consulted

only for commands the local policy already allows, so it can refuse more but

never widen. Widening happens here or not at all.

Command Classification

Every command is classified before execution:

• read-only: Allowlisted commands (ls, cat, grep, df, stat, systemctl status, ...)
• safe: Non-destructive mutations (npm install, git pull, ...)
• destructive: mutations that need approval (rm -rf /tmp/build, ...)
• privileged: sudo, su, doas, pkexec

A separate forbidden list is never allowed, whatever the role or approval

policy: rm -rf /, mkfs, dd of=/dev/, shutdown, curl|sh, fork bombs,

writes to /etc/cron, /etc/systemd or authorized_keys, iptables -F, and

recursive chmod 777 / / chown /. Add your own patterns via the policy

denylist; an invalid pattern fails at startup rather than degrading silently.

Approval Modes

• auto — no prompts (dev only!)
• ask-destructive — prompt for destructive/privileged (default)
• ask-all — prompt for every command
• deny — reject destructive/privileged commands outright (no prompt)

Approval Grants (just-in-time)

approvalGrantTtlMs lets one explicit approval cover repeats of the **exact

same** command on the same profile for a bounded time (e.g. 300000 for five

minutes). It exists because approving rm -rf /tmp/build every few seconds

during an iterative task trains you to click through prompts — which is worse

for safety than a grant you chose deliberately.

A grant is bound to the exact command text, the profile and the command class:

approving rm -rf /tmp/build does not cover rm -rf /tmp/build-prod, the same

command on another host, or the same command escalated to sudo. Runs covered

by a grant appear in the audit log with approver: "jit-grant", so they stay

distinguishable from a fresh human answer.

Off by default (0 = always prompt). Auto-approval weakens the gate that

makes destructive commands safe, so turning it on should be a decision.

Answering the prompt

Approval goes through the MCP elicitation request, so what you see is your

client's dialog. Accepting it approves the command — there is no second field to

fill in.

You have 10 minutes to answer. Past that the request expires and the command

is refused rather than left pending, and the refusal says so; the prompt may

still be open in your client, in which case run the command again once you are

ready. If your client does not support elicitation at all, every destructive and

privileged command is refused with APPROVAL_UNAVAILABLE naming that cause —

approval fails closed by design.

Command Quota

commandQuotaPerDay bounds how many commands a profile may run in a rolling

24-hour window (0 = unlimited). The approval gate stops *destructive* commands

and the HTTP rate limiter caps request rate, but neither bounds total work — a

prompt-injected agent looping over allowed commands stays under both. The quota

is the circuit breaker for that case.

Counted after policy allows a command and before it runs, so a denied command

does not spend budget. The window slides rather than resetting at midnight,

which would let an agent spend a full quota just before the reset and another

immediately after.

External Policy Engine (OPA)

For organizations that standardize on Open Policy Agent / Rego:

ssh-mcp --opaUrl=http://localhost:8181

When --opaUrl is set, commands the built-in engine allows are additionally

evaluated by OPA. OPA can only narrow. A command the built-in engine has

already denied returns that denial without OPA being consulted at all, so a

sidecar answering allow cannot grant a class the role bindings withhold. To

widen, edit [policy]. The request shape follows the AuthZEN Access Evaluation contract:

{
  "input": {
    "subject": { "role": "operator", "profile": "prod-web-1" },
    "action": { "tool": "run-command", "commandClass": "destructive" },
    "resource": { "command": "rm -rf /tmp/cache", "binary": "rm", "host": "10.0.1.50" },
    "context": { "readOnly": false }
  }
}

OPA responds with { "result": true/false }. If OPA denies (result: false), the command is blocked even if the built-in engine allows it. If OPA is unreachable, the built-in engine's decision stands (fail-open to avoid locking out access).

Example Rego policy (ssh-mcp.rego):

package ssh.mcp

default allow := false

# Admins pass the OPA gate on dev hosts. The built-in policy still applies on
# top: this widens nothing that the role bindings withhold.
allow if {
  input.subject.role == "admin"
  startswith(input.subject.profile, "dev")
}

# Deny all destructive commands on prod
deny if {
  input.action.commandClass == "destructive"
  startswith(input.subject.profile, "prod")
}

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Security

Threat Model

See SECURITY.md for the full threat model, vulnerability reporting policy, and deployment checklist.

Safe Defaults

• Non-root user in all examples
• TOFU host key verification (accept on first connect, verify after)
• RFC 9142 algorithm allow-list (no SHA-1, no CBC, no ssh-rsa)
• exec()-only (no persistent su shells — fixes PTY leak)
• Sudo via stdin (not argv — fixes process list leak)
• Sanitizer strips CR/LF/NUL from all metadata
• 3-layer redaction (field → regex → entropy) on audit logs
• No CLI-arg secrets (use env vars, keychain, or config)

Hardening Checklist

• [ ] Create dedicated low-privilege service account on target hosts
• [ ] Use command-specific sudoers instead of NOPASSWD: ALL
• [ ] Enable ask-all approval for production profiles
• [ ] Restrict network egress on target hosts
• [ ] Use readOnly = true for monitoring profiles
• [ ] Review audit logs regularly
• [ ] Run chmod 600 config.toml

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Transports

stdio (default)

For local MCP clients (Claude Code, Cursor, Windsurf). No network exposure.

ssh-mcp                          # reads config from XDG path
ssh-mcp --config=/path/to.toml   # custom config path

HTTP (optional)

For remote/web clients behind a reverse proxy with TLS:

ssh-mcp --transport=http --httpPort=3000 --bearerToken=secret
ssh-mcp --transport=http --httpPort=3000 --bearerToken=secret --rateLimit=60

Endpoints: POST / (MCP Streamable HTTP), GET /status, GET /health

When rate limit is exceeded, the server returns HTTP 429 with Retry-After header and a JSON-RPC error body so MCP clients can handle it gracefully.

Always terminate TLS at a reverse proxy (Caddy/nginx). The server listens on 127.0.0.1 only.

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Docker

# Build
docker build -t ssh-mcp .

# Run (config file + env vars for credentials)
docker run -i \
  -v ./config.toml:/home/appuser/.config/ssh-mcp/config.toml:ro \
  -e SSH_MCP_PASSWORD=secret \
  ssh-mcp

Or with docker-compose:

docker-compose --profile app up

The Docker image runs as non-root UID 65532, with a minimal node:22-slim base.

---

CLI Flags (v2)

Secrets are never passed as CLI arguments.

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Migrating from v1

v2 is a breaking release. Passing a removed flag now fails at startup with the

replacement, rather than failing later as a confusing auth error.

Tools

Command results now carry status. In v1 a failed command rejected with

Error (code N). In v2 a non-zero exit comes back as an error result including

the exit code and stderr — so an empty response no longer means "it worked".

Flags

Credentials moved off the command line because CLI arguments are world-readable

via /proc//cmdline on Linux (CWE-214). Credentials now resolve through an

SSH agent → OS keychain → env var → key file cascade.

Example

// v1
{ "command": "npx", "args": ["ssh-mcp", "--host=1.2.3.4", "--user=root", "--password=hunter2"] }

// v2 — credentials via env
{
  "command": "npx",
  "args": ["ssh-mcp", "--host=1.2.3.4", "--user=root"],
  "env": { "SSH_MCP_PASSWORD": "hunter2" }
}

For more than one host, move to a TOML config file (see Configuration)

and pass --config ; profiles carry per-host roles and approval policy.

Host key verification

v1 did not verify host keys. v2 defaults to trust-on-first-use and records the

key; a later mismatch fails the connection. Pin explicitly with trustedHostKey

in a profile, or pass --insecureHostKey to opt out (test environments only).

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Testing

# Start test SSH server
docker-compose --profile test up -d

# Run all tests
npm test

# Run only unit tests
npm test -- test/unit/

# Run with coverage
npm run coverage

MCP Inspector

npm run inspect

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Contributing

See CONTRIBUTING.md. Please follow the security checklist in all PRs.

Support

If you find SSH MCP Server helpful, consider starring the repository or sponsoring!