Proxmox VE Hardening Guide

By Bearloggs
proxmox hardening linux devsecops

Proxmox VE Hardening Guide#

Secure your Proxmox VE for Internet exposure using both OS- and application-level defenses: a random high-numbered SSH port, strict UFW firewalling, WireGuard VPN, and only VPN-based access for admin and SSH.

⚠️ Warning: This Is Not an Exhaustive Security Checklist

  • This guide covers essential steps for securing your server, but it is not a complete or exhaustive list of all possible security measures.
  • Your specific environment may require additional precautions. Review all relevant documentation, stay informed about current vulnerabilities, and regularly update your security practices.
  • Be extremely careful: Changing firewall, SSH, or VPN settings can lock you out if misconfigured. Always test changes in a separate session and ensure you have a way to recover access (such as console, KVM, or rescue mode) before proceeding.

Keep Debian and Proxmox Patched#

Stay up to date—for OS security and software bug fixes:

sudo apt update && sudo apt full-upgrade -y
sudo apt autoremove -y

Create a Non-root Admin User#

Use a separate, non-root admin account for remote access/administration:

sudo adduser adminuser
sudo usermod -aG sudo adminuser

Replace adminuser with your username of choice.

Set up strong SSH keys (on your laptop):

ssh-copy-id adminuser@your.server.ip

Or manually add your public key to /home/adminuser/.ssh/authorized_keys.

Test login:

ssh adminuser@your.server.ip

Before proceeding, make sure key login for the new user works!

Harden SSH: Custom High Port, No Root Password Logins#

Choose a Unique, High SSH Port#

  • Pick an unused, random port between 49152–65535. Check open ports:
sudo ss -tuln
  • Suppose you use 54321.

Edit SSH Config#

/etc/ssh/sshd_config

Port 54321
PermitRootLogin no
PasswordAuthentication no
AllowUsers adminuser
MaxAuthTries 3
LoginGraceTime 30

Restart and TEST SSH:

sudo systemctl reload ssh
ssh -p 54321 adminuser@your.server.ip

Do not lock yourself out!

Lock Down the UFW Firewall#

Install UFW and set defaults:

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

Allow only your new SSH port (for initial remote admin):

sudo ufw allow 54321/tcp

You’ll further restrict this after VPN is set up.

Enable Two-Factor Authentication (2FA) for Proxmox#

  1. In Proxmox web UI:
    Datacenter > Users > Select user > Set “2nd Factor” (TOTP).
  2. Pair 2FA (Google Authenticator, Authy, etc.) with all admin accounts.

WireGuard VPN — Only Admin Access via VPN#

Install and Configure WireGuard#

a) Install:

sudo apt install wireguard -y

b) Generate VPN server keys:

umask 077
wg genkey | tee server_private.key | wg pubkey > server_public.key

(Repeat on each client to generate individual keys)

c) Configure WireGuard server (/etc/wireguard/wg0.conf):

[Interface]
Address = 10.10.10.1/24
ListenPort = 51820
PrivateKey = (server_private.key contents)

# Add a [Peer] section for each client:
[Peer]
PublicKey = (client_public_key)
AllowedIPs = 10.10.10.2/32

d) Enable IP Forwarding:

echo "net.ipv4.ip_forward=1" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

e) Start and Enable WireGuard:

sudo systemctl enable wg-quick@wg0
sudo systemctl start wg-quick@wg0

f) Client example config:

[Interface]
PrivateKey = (client_private)
Address = 10.10.10.2/24

[Peer]
PublicKey = (server_public)
Endpoint = your.server.ip:51820
AllowedIPs = 10.10.10.1/32
PersistentKeepalive = 25

Restrict Admin Interfaces to VPN Only with UFW#

After VPN is fully connected and tested:

sudo ufw allow 51820/udp                                  # Allow VPN
sudo ufw allow from 10.10.10.0/24 to any port 8006        # Proxmox web GUI from VPN only
sudo ufw allow from 10.10.10.0/24 to any port 54321       # SSH from VPN only
sudo ufw deny 8006/tcp                                    # Block GUI from public
sudo ufw deny 54321/tcp                                   # Block SSH from public
sudo ufw enable
sudo ufw status verbose

Now, only the VPN subnet can access SSH and GUI. VPN is your admin “door.”

Enable Proxmox Firewall Feature#

  • In Proxmox web UI:
    • Datacenter → Firewall → Enable.
    • Enable on nodes and VMs as needed.
    • Default: DROP all, and explicitly ALLOW only from VPN subnet.

Monitor, Audit, Respond#

  • Check system and Proxmox logs regularly: 
    sudo journalctl -xe
sudo tail -f /var/log/auth.log
sudo tail -f /var/log/pveproxy/access.log
  • Install Fail2Ban to block brute-force SSH attempts: 
    sudo apt install fail2ban
  • Periodically review user accounts, VPN keys, and firewall rules.

Ongoing Security Checklist#

  • Debian & Proxmox regularly patched
  • Non-root sudo admin with SSH key only
  • Random high, unused SSH port
  • SSH: root login denied, passwords off
  • UFW: VPN subnet is only way to reach Proxmox GUI/SSH
  • 2FA enforced for admin users
  • WireGuard VPN required for any admin access
  • Proxmox built-in firewall is enabled
  • Fail2Ban and system logging active

How to Manage UFW Firewall Rules#

  • Check active rules: 
    sudo ufw status verbose
  • List rules, numbered (for easy removal): 
    sudo ufw status numbered
  • Remove by number: 
    sudo ufw delete <number>
  • Remove by rule: 
    sudo ufw delete allow 51820/udp

Quick Recap#

  • All management traffic must traverse your VPN.
  • Nothing (SSH, GUI, etc.) is exposed to the public Internet.
  • Regularly log in to your VPN with WireGuard before accessing the web GUI or SSH.
  • Periodically review firewall rules, update your system, and check your audit logs.

Further Resources#