Security Hardening: Linux Host for OpenClaw

Tested on

Ubuntu 24.04 LTS (bare metal, Intel Ultra 250, 64GB DDR5)

Last updated

2026-04-19

Practical hardening runbook for an Ubuntu 24.04 machine running OpenClaw as an always-on AI agent. This covers firewall configuration, SSH lockdown, fail2ban, and service binding to reduce attack surface.

Why This Matters

An OpenClaw host is a high-value target. It has API keys for AI providers, access to your messaging platforms, and potentially SSH access to other machines. Default Linux configurations are permissive. This guide reduces the attack surface to what’s actually needed.

Overview of Changes

1. UFW Firewall

Install and Enable

sudo apt install ufw -y
sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw enable

Rule Set

Replace <LAN_SUBNET_CIDR> with your LAN subnet. Replace <HOST_LAN_IP> with your host’s LAN IP.

# SSH - LAN only
sudo ufw allow from <LAN_SUBNET_CIDR> to any port 22 proto tcp

# Web traffic (if running any web services publicly)
sudo ufw allow 80/tcp
sudo ufw allow 443/tcp

# Dev server ports - LAN only
sudo ufw allow from <LAN_SUBNET_CIDR> to any port 5173:5214 proto tcp

# Ops Deck API - LAN only
sudo ufw allow from <LAN_SUBNET_CIDR> to any port 8005 proto tcp

# OpenClaw Gateway - LAN only
sudo ufw allow from <LAN_SUBNET_CIDR> to any port 18789 proto tcp

# Ollama - deny from everywhere (defense-in-depth, already localhost-bound)
sudo ufw deny 11434

# mDNS - LAN only
sudo ufw allow from <LAN_SUBNET_CIDR> to any port 5353 proto udp

Verify

sudo ufw status verbose

Expected output should show Status: active, Default: deny (incoming), and your explicit allow/deny rules.

2. SSH Hardening

The Problem

Default Ubuntu SSH configuration:

• Listens on 0.0.0.0:22 and [::]:22 (all interfaces)
• Password authentication enabled
• Root login permitted
• 6 max authentication tries

The Fix

Create a drop-in config (cleaner than editing the main sshd_config, easier to audit and roll back):

sudo tee /etc/ssh/sshd_config.d/hardening.conf << 'EOF'
# OpenClaw host hardening - 2026-03-11
PasswordAuthentication no
PermitRootLogin no
MaxAuthTries 3
EOF

Ubuntu 24.04 Gotcha: Socket Activation

Ubuntu 24.04 uses systemd socket activation for SSH. This means ListenAddress in sshd_config is ignored when ssh.socket is active. You need a socket override:

sudo mkdir -p /etc/systemd/system/ssh.socket.d
sudo tee /etc/systemd/system/ssh.socket.d/override.conf << 'EOF'
[Socket]
# Clear default ListenStream (0.0.0.0:22 and [::]:22)
ListenStream=
# Bind to LAN IP only
ListenStream=<HOST_LAN_IP>:22
EOF

sudo systemctl daemon-reload
sudo systemctl restart ssh.socket

Note: The empty ListenStream= line is required. It clears the default listen addresses before setting the new one. Without it, your custom address gets added to the defaults instead of replacing them.

Verify

# Check listening address
ss -tlnp | grep :22

# Should show only your LAN IP, not 0.0.0.0 or [::]
# Expected: <HOST_LAN_IP>:22

# Check config values
sudo sshd -T | grep -E "passwordauthentication|permitrootlogin|maxauthtries"

# Expected:
# passwordauthentication no
# permitrootlogin no
# maxauthtries 3

3. fail2ban

Install and Configure

sudo apt install fail2ban -y

Create a local jail config (never edit jail.conf directly, it gets overwritten on updates):

sudo tee /etc/fail2ban/jail.local << 'EOF'
[sshd]
enabled = true
port = ssh
filter = sshd
maxretry = 3
bantime = 7200
findtime = 600
EOF

sudo systemctl enable fail2ban
sudo systemctl restart fail2ban

This gives you:

• 3 failed attempts within a 10-minute window triggers a ban
• 2-hour ban per offense
• Covers both password and key auth failures

Verify

sudo fail2ban-client status sshd

Expected: Status for the jail: sshd with Currently banned: 0 (on a fresh setup).

4. xrdp (Remote Desktop)

If you run xrdp for remote desktop access, bind it to your LAN IP instead of all interfaces.

The Fix

Edit /etc/xrdp/xrdp.ini, find the port= line (typically line 23):

# Before
port=3389

# After
port=tcp://<HOST_LAN_IP>:3389

Note: xrdp uses port=tcp://host:port syntax, not address= as some documentation suggests. This is a common gotcha.

sudo systemctl restart xrdp

Verify

ss -tlnp | grep :3389

# Should show <HOST_LAN_IP>:3389, not 0.0.0.0:3389

5. OpenClaw Gateway

The OpenClaw gateway (default port 18789) binds to 0.0.0.0 by default. Rather than changing the gateway config, we protect it at the firewall level:

# Already covered by the UFW rules above
sudo ufw allow from <LAN_SUBNET_CIDR> to any port 18789 proto tcp

This keeps the gateway accessible from your LAN but blocks external access.

6. Ollama (Defense-in-Depth)

Ollama binds to 127.0.0.1:11434 by default, which is already correct. The UFW deny rule is defense-in-depth in case the binding ever changes:

sudo ufw deny 11434

This costs nothing and protects against configuration drift.

Full Verification Script

Run this after applying all changes to confirm everything is locked down:

#!/bin/bash
echo "=== SSH Binding ==="
ss -tlnp | grep :22

echo ""
echo "=== xrdp Binding ==="
ss -tlnp | grep :3389

echo ""
echo "=== SSH Config ==="
sudo sshd -T 2>/dev/null | grep -E "passwordauthentication|permitrootlogin|maxauthtries"

echo ""
echo "=== UFW Status ==="
sudo ufw status | head -20

echo ""
echo "=== fail2ban Status ==="
sudo fail2ban-client status sshd 2>/dev/null || echo "fail2ban not running"

Expected output:

SSH: <HOST_LAN_IP>:22 only
xrdp: <HOST_LAN_IP>:3389 only
sshd: PasswordAuthentication no, PermitRootLogin no, MaxAuthTries 3
UFW: active, default deny incoming
fail2ban: sshd jail active, 0 banned

What This Doesn’t Cover

• Automatic security updates (configure unattended-upgrades)
• Kernel hardening (sysctl parameters, AppArmor profiles)
• Audit logging (auditd rules for sensitive file access)
• Network segmentation (VLANs, separate management interfaces)
• Intrusion detection (host-based IDS like OSSEC/Wazuh)

These are all good next steps depending on your threat model. This guide focuses on the fundamentals that every OpenClaw host should have on day one.

Implementation Notes

1. Drop-in configs over main configs. Using /etc/ssh/sshd_config.d/hardening.conf instead of editing /etc/ssh/sshd_config makes auditing and rollback trivial. You can ls the .d directory and see exactly what changed and when.

2. Socket activation is the future. Ubuntu 24.04’s move to ssh.socket activation catches a lot of people off guard. The ListenAddress directive in sshd_config does nothing when the socket unit is active. Always check systemctl status ssh.socket first.

3. Defense-in-depth is cheap. The Ollama deny rule costs nothing and protects against drift. Apply this pattern to any service that should stay localhost-only.

4. Test from another machine. After applying SSH changes, keep your current session open and test a new connection from a different machine. If you lock yourself out, the existing session still works.

5. OpenClaw upgrades regenerate the systemd unit. Every minor upgrade across the 2026.4.x line has silently regenerated ~/.config/systemd/user/openclaw-gateway.service and dropped custom directives - most painfully EnvironmentFile=. Without it, secrets from ~/.openclaw/workspace/.env don’t load and the gateway crash-loops. If you maintain a hardening script, run it after every openclaw update, or automate the restore. We use a wrapper script (~/bin/openclaw-update.sh) that bumps the version drop-in and re-asserts EnvironmentFile= after each upgrade.