tufantunc/ssh-mcp

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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.

---

Quick Start

1. Install

npm install -g ssh-mcp

2. Configure

Create the config file at the path for your platform:

Platform	Path
Linux	~/.config/ssh-mcp/config.toml (or $XDG_CONFIG_HOME/ssh-mcp/config.toml)
macOS	~/Library/Application Support/ssh-mcp/config.toml
Windows	%APPDATA%\ssh-mcp\config.toml

[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 700 ~/.config/ssh-mcp && chmod 600 ~/.config/ssh-mcp/config.toml

The config decides which hosts, roles and policy rules this server honours, so it checks that nobody but you can read it — and treats the two platforms differently, because the question has a much clearer answer on one of them.

Linux and macOS: enforced. The mode check above, on the file and the directory — which is why chmod 700 is in that command, since mkdir -p under the default umask leaves the directory 0755. The server refuses to start otherwise. "Only the owner" is unambiguous here and chmod is a one-line fix.

Windows: split by what the ACL actually allows. There are no mode bits, so the ACL is read instead — and read exposure and write exposure are not treated alike, because Windows is much clearer about one of them than the other.

The ACL lets another account…	Default
only read the config	reported, and the server starts
change the config	refused
nothing (no ACL at all)	refused — that is full control for everyone
…and if the ACL could not be read	refused, except when icacls is absent or the check timed out

A config under %APPDATA% inherits access for you, SYSTEM and Administrators and needs nothing done to it. One created elsewhere does not: a file under C:\ inherits *read* for every local account and *modify* for every authenticated one. The message names the two icacls commands that fix it either way.

Read exposure is reported rather than refused because that is where Windows is genuinely muddier than POSIX, and refusing over it blocked a config at the documented location (#138). Write exposure is refused because it is not muddy at all: another account being able to rewrite the file that decides which hosts, roles and approval policy this server honours is an authorization bypass, not a disclosure.

Two flags move the whole thing: --strictConfigAcl refuses everything the check objects to, read-only grants included; --allowUncheckedConfigAcl reports everything and refuses nothing. Neither combination leaves you without an exit, which is the lesson of #138.

Exit statuses

Status	Meaning
0	Clean shutdown
1	A defect in the server — printed with a stack trace; please report it
2	How it was invoked or configured — printed as a message, no stack

A supervisor that treats any non-zero status as a failure needs no change. One that matched on 1 to detect a startup problem should match on 2 as well.

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.

---

Tools (11)

Tool	Purpose	readOnly	destructive
list-connections	Discover available hosts and connection status	✅	—
list-sessions	List active sessions per host	✅	—
open-session	Create a named interactive (stateful) or background session	—	—
close-session	Close a session, releasing resources	—	✅
read-session-output	Read output from background sessions (e.g., tail -f)	✅	—
read-command	Execute allowlisted read-only commands (ls, cat, grep, ...)	✅	—
run-command	Execute arbitrary commands (destructive ones need approval)	—	—
privileged-command	Execute with sudo (always requires approval)	—	✅
sftp-upload	Upload a file via SFTP	—	✅
sftp-download	Download a file via SFTP	✅	—
signal-process	Send INT/TERM/KILL to a remote PID	—	✅

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.

	Linux / BSD / macOS	Windows OpenSSH
read-command, run-command, privileged-command, signal-process	✅	✅
sftp-upload, sftp-download	✅	✅
Background sessions	✅	✅
Interactive sessions	✅	❌

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.

---

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_<NAME>_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_<NAME>_PASSWORD
4. Key file — keyRef path or SSH_MCP_KEY env var

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

---

Policy Engine

Roles

Role	Dev	Staging	Prod
viewer	read-only	read-only	read-only
operator	read-only, safe, destructive	read-only, safe, destructive	read-only, safe
admin	all	all	read-only, safe, destructive

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")
}

---

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 700 <config dir> && chmod 600 config.toml (Windows: the ACL under %APPDATA% is already restricted)

---

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

Flag	Default	Description
--bearerToken	required	Bearer token for authentication (all routes except GET /health)
--httpPort	3000	HTTP listen port
--httpHost	127.0.0.1	Bind address
--rateLimit	0 (off)	Max requests per minute (0 = unlimited)

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.

---

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.

Flag	Default	Description
--config	platform config dir (see Configure)	Path to TOML config file
--host	—	Quick start: SSH host (creates single-profile config)
--user	—	Quick start: SSH username
--port	22	Quick start: SSH port
--key	—	Quick start: Path to private key
--workdir	—	Quick start: Working directory for commands and sessions
--group	prod	Quick start: Policy tier — prod, staging or dev
--timeout	60000	Command timeout in ms
--maxChars	5000	Max command length (none or 0 disables the limit; in a config file the same setting is commandMaxChars = 0)
--sessionMax	5	Max concurrent sessions per connection
--sessionTtl	600000	Session idle timeout in ms
--transport	stdio	stdio or http
--httpPort	3000	HTTP transport port
--httpHost	127.0.0.1	HTTP bind address
--bearerToken	—	Bearer token for HTTP transport auth (required for --transport=http)
--rateLimit	0	HTTP requests per minute on the MCP route (0 = unlimited)
--allowedHosts	bind address + localhost	Comma-separated Host headers accepted by the DNS-rebinding guard
--insecureHostKey	false	Disable host key verification (test only!)
--allowUncheckedConfigAcl	false	Windows: report every ACL finding and refuse none
--strictConfigAcl	false	Windows: refuse on every ACL finding, including a read-only over-grant
--disableApproval	false	Skip the approval gate (quick start profile only)
--opaUrl	—	OPA sidecar URL for external policy
--commandQuota	0 (off)	Max commands per rolling 24h per profile
--approvalGrantTtl	0 (off)	Auto-approve an identical command for this many ms after approval
--auditEntropyScan	false	Enable entropy-based secret scanning in audit
--auditTamperEvident	false	Enable hash-chained tamper-evident audit log
--otelEndpoint	—	OTLP/HTTP endpoint for OpenTelemetry traces
--otelServiceName	ssh-mcp	Service name reported on trace spans
--dumpToolHashes	—	Print SHA-256 hashes of the tool descriptions and exit

---

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

v1	v2	Notes
exec	read-command	Allowlisted read-only commands. Prefer this for reads.
exec	run-command	Arbitrary commands. Destructive ones go through the approval gate.
sudo-exec	privileged-command	Always requires approval. Password is piped via stdin.
description parameter	—	Removed. It was an injection vector (#44) and never reached the host.

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

v1 flag	Replacement
--password	SSH_MCP_PASSWORD env var (or SSH_MCP_<PROFILE>_PASSWORD)
--suPassword	SSH_MCP_SUDO_PASSWORD env var
--sudoPassword	SSH_MCP_SUDO_PASSWORD env var
--disableSudo	Use a role/policy that disallows the privileged class

Credentials moved off the command line because CLI arguments are world-readable via /proc/<pid>/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 <path>; 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).

---

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

---

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!