Security Best Practices for your ETH staking validator node

Quick steps to secure your node.

🤖 Pre-requisites

• Ubuntu Server or Ubuntu Desktop installed

• SSH server installed

• a SSH client or terminal window access

In case you need to install SSH server, refer to:

How to install SSH server on Ubuntu

In case you need a SSH client for your operating system, refer to:

How to Connect to an SSH Server from Windows, macOS, or LinuxHow-To Geek

🧙‍♂️Create a non-root user with sudo privileges

Make a habit of logging to your server using a non-root account. This will prevent the accidental deletion of files if you make a mistake. For instance, the command rm can wipe your entire server if run incorrectly using by a root user.

🔥Tip: Do NOT routinely use the root account. Use su or sudo, always.

SSH to your server with your SSH client

ssh [e-mail]
# example
# ssh myUsername@77.22.161.10

Create a new user called ethereum

sudo useradd -m -s /bin/bash ethereum

Set the password for ethereum user

sudo passwd ethereum

Add ethereum to the sudo group

sudo usermod -aG sudo ethereum

🔐 Disable SSH password Authentication and Use SSH Keys only

The basic rules of hardening SSH are:

• No password for SSH access (use private key)

• Don't allow root to SSH (the appropriate users should SSH in, then su or sudo)

• Use sudo for users so commands are logged

• Log unauthorized login attempts (and consider software to block/ban users who try to access your server too many times, like fail2ban)

• Lock down SSH to only the ip range your require (if you feel like it)

Create a new SSH key pair on your local machine. Run this on your local machine. You will be asked to type a file name in which to save the key. This will be your keyname.

Your choice of ED25519 or RSA public key algorithm.

ED25519

ssh-keygen -t ed25519

RSA

ssh-keygen -t rsa -b 4096

Transfer the public key to your remote node. Update keyname.pub appropriately.

ssh-copy-id -i $HOME/.ssh/keyname.pub [e-mail]

Login with your new ethereum user

ssh [e-mail]

Disable root login and password based login. Edit the /etc/ssh/sshd_config file

sudo nano /etc/ssh/sshd_config

Locate ChallengeResponseAuthentication and update to no

ChallengeResponseAuthentication no

Locate PasswordAuthentication update to no

PasswordAuthentication no

Locate PermitRootLogin and update to prohibit-password

PermitRootLogin prohibit-password

Locate PermitEmptyPasswords and update to no

PermitEmptyPasswords no

Optional: Locate Port and customize it your random port.

Use a random port # from 1024 thru 49141. Check for possible conflicts.

Port <port number>

Validate the syntax of your new SSH configuration.

sudo sshd -t

If no errors with the syntax validation, restart the SSH process

sudo systemctl restart sshd

Verify the login still works

Standard SSH Port 22

ssh [e-mail]

Custom SSH Port

ssh [e-mail] -p <custom port number>

Alternatively, you might need to add the -p <port#> flag if you used a custom SSH port.

ssh -i <path to your SSH_key_name.pub> [e-mail]

Optional: Make logging in easier by updating your local ssh config.

To simplify the ssh command needed to log in to your server, consider updating your local $HOME/.ssh/config file:

Host ethereum-server
  User ethereum
  HostName <server.public.ip.address>
  Port <custom port number>

This will allow you to log in with ssh ethereum-server rather than needing to pass through all ssh parameters explicitly.

🤖 Update your system

It's critically important to keep your system up-to-date with the latest patches to prevent intruders from accessing your system.

sudo apt-get update -y && sudo apt dist-upgrade -y
sudo apt-get autoremove
sudo apt-get autoclean

Enable automatic updates so you don't have to manually install them.

sudo apt-get install unattended-upgrades
sudo dpkg-reconfigure -plow unattended-upgrades

🐻 Disable root account

System admins should not frequently log in as root in order to maintain server security. Instead, you can use sudo execute that require low-level privileges.

# To disable the root account, simply use the -l option.
sudo passwd -l root

# If for some valid reason you need to re-enable the account, simply use the -u option.
sudo passwd -u root

🛠️ Setup Two Factor Authentication for SSH [Optional]

SSH, the secure shell, is often used to access remote Linux systems. Because we often use it to connect with computers containing important data, it’s recommended to add another security layer. Here comes the two factor authentication (2FA).

sudo apt install libpam-google-authenticator -y

To make SSH use the Google Authenticator PAM module, edit the /etc/pam.d/sshd file:

sudo nano /etc/pam.d/sshd

Add the following line:

auth required pam_google_authenticator.so

Now you need to restart the sshd daemon using:

sudo systemctl restart sshd.service

Modify /etc/ssh/sshd_config

sudo nano /etc/ssh/sshd_config

Locate ChallengeResponseAuthentication and update to yes

ChallengeResponseAuthentication yes

Locate UsePAM and update to yes

UsePAM yes

Save the file and exit.

Run the google-authenticator command.

google-authenticator

It will ask you a series of questions, here is a recommended configuration:

• Make tokens “time-base”": yes

• Update the .google_authenticator file: yes

• Disallow multiple uses: yes

• Increase the original generation time limit: no

• Enable rate-limiting: yes

You may have noticed the giant QR code that appeared during the process, underneath are your emergency scratch codes to be used if you don’t have access to your phone: write them down on paper and keep them in a safe place.

Now, open Google Authenticator on your phone and add your secret key to make two factor authentication work.

Note: If you are enabling 2FA on a remote machine that you access over SSH you need to follow steps 2 and 3 of this tutorial to make 2FA work.

🧩 Secure Shared Memory

One of the first things you should do is secure the shared memory used on the system. If you're unaware, shared memory can be used in an attack against a running service. Because of this, secure that portion of system memory.

To learn more about secure shared memory, read this techrepublic.com article.

One exceptional case

There may be a reason for you needing to have that memory space mounted in read/write mode (such as a specific server application like DappNode that requires such access to the shared memory or standard applications like Google Chrome). In this case, use the following line for the fstab file with instructions below.

none /run/shm tmpfs rw,noexec,nosuid,nodev 0 0

The above line will mount the shared memory with read/write access but without permission to execute programs, change the UID of running programs, or to create block or character devices in the namespace. This a net security improvement over default settings.

Use with caution

With some trial and error, you may discover some applications(like DappNode) do not work with shared memory in read-only mode. For the highest security and if compatible with your applications, it is a worthwhile endeavor to implement this secure shared memory setting.

Source: techrepublic.com

Edit /etc/fstab

sudo nano /etc/fstab

Insert the following line to the bottom of the file and save/close. This sets shared memory into read-only mode.

tmpfs    /run/shm    tmpfs    ro,noexec,nosuid    0 0

Reboot the node in order for changes to take effect.

sudo reboot

⛓️Install Fail2ban

Fail2ban is an intrusion-prevention system that monitors log files and searches for particular patterns that correspond to a failed login attempt. If a certain number of failed logins are detected from a specific IP address (within a specified amount of time), fail2ban blocks access from that IP address.

sudo apt-get install fail2ban -y

Edit a config file that monitors SSH logins.

sudo nano /etc/fail2ban/jail.local

Add the following lines to the bottom of the file.

🔥 Whitelisting IP address tip: The ignoreip parameter accepts IP addresses, IP ranges or DNS hosts that you can specify to be allowed to connect. This is where you want to specify your local machine, local IP range or local domain, separated by spaces.

# Example
ignoreip = 192.168.1.0/24 127.0.0.1/8 

[sshd]
enabled = true
port = <22 or your random port number>
filter = sshd
logpath = /var/log/auth.log
maxretry = 3
# whitelisted IP addresses
ignoreip = <list of whitelisted IP address, your local daily laptop/pc>

Save/close file.

Restart fail2ban for settings to take effect.

sudo systemctl restart fail2ban

🧱Configure your Firewall

The standard UFW firewall can be used to control network access to your node.

With any new installation, ufw is disabled by default. Enable it with the following settings.

• Port 22 (or your random port #) TCP for SSH connection

• Ports for p2p traffic

  • Lighthouse uses port 9000 tcp/udp

  • Teku uses port 9000 tcp/udp

  • Prysm uses port 13000 tcp and port 12000 udp

  • Nimbus uses port 9000 tcp/udp

  • Lodestar uses port 30607 tcp and port 9000 udp

• Port 30303 tcp/udp eth1 node

Lighthouse

# By default, deny all incoming and outgoing traffic
sudo ufw default deny incoming
sudo ufw default allow outgoing
# Allow ssh access
sudo ufw allow ssh #<port 22 or your random ssh port number>/tcp
# Allow p2p ports
sudo ufw allow 9000/tcp
sudo ufw allow 9000/udp
# Allow eth1 port
sudo ufw allow 30303/tcp
sudo ufw allow 30303/udp
# Enable firewall
sudo ufw enable

Prysm

# By default, deny all incoming and outgoing traffic
sudo ufw default deny incoming
sudo ufw default allow outgoing
# Allow ssh access
sudo ufw allow ssh #<port 22 or your random ssh port number>/tcp
# Allow p2p ports
sudo ufw allow 13000/tcp
sudo ufw allow 12000/udp
# Allow eth1 port
sudo ufw allow 30303/tcp
sudo ufw allow 30303/udp
# Enable firewall
sudo ufw enable

Teku

# By default, deny all incoming and outgoing traffic
sudo ufw default deny incoming
sudo ufw default allow outgoing
# Allow ssh access
sudo ufw allow ssh #<port 22 or your random ssh port number>/tcp
# Allow p2p ports
sudo ufw allow 9000/tcp
sudo ufw allow 9000/udp
# Allow eth1 port
sudo ufw allow 30303/tcp
sudo ufw allow 30303/udp
# Enable firewall
sudo ufw enable

Nimbus

# By default, deny all incoming and outgoing traffic
sudo ufw default deny incoming
sudo ufw default allow outgoing
# Allow ssh access
sudo ufw allow ssh #<port 22 or your random ssh port number>/tcp
# Allow p2p ports
sudo ufw allow 9000/tcp
sudo ufw allow 9000/udp
# Allow eth1 port
sudo ufw allow 30303/tcp
sudo ufw allow 30303/udp
# Enable firewall
sudo ufw enable

Lodestar

# By default, deny all incoming and outgoing traffic
sudo ufw default deny incoming
sudo ufw default allow outgoing
# Allow ssh access
sudo ufw allow ssh #<port 22 or your random ssh port number>/tcp
# Allow p2p ports
sudo ufw allow 30607/tcp
sudo ufw allow 9000/udp
# Allow eth1 port
sudo ufw allow 30303/tcp
sudo ufw allow 30303/udp
# Enable firewall
sudo ufw enable

# Verify status
sudo ufw status numbered

Do not expose Grafana (port 3000) and Prometheus endpoint (port 9090) to the public internet as this invites a new attack surface! A secure solution would be to access Grafana through a ssh tunnel with Wireguard.

Only open the following ports on local home staking setups behind a home router firewall or other network firewall.

🔥 It is dangerous to open these ports on a VPS/cloud node.

# Allow grafana web server port
sudo ufw allow 3000/tcp
# Enable prometheus endpoint port
sudo ufw allow 9090/tcp

Confirm the settings are in effect.

# Verify status
sudo ufw status numbered
     To                         Action      From
     --                         ------      ----
[ 1] 22/tcp                     ALLOW IN    Anywhere
# SSH
[ 2] 3000/tcp                   ALLOW IN    Anywhere
# Grafana
[ 3] 9000/tcp                   ALLOW IN    Anywhere
# eth2 p2p traffic
[ 4] 9090/tcp                   ALLOW IN    Anywhere
# Prometheus
[ 5] 30303/tcp                  ALLOW IN    Anywhere
# eth1 node
[ 6] 22/tcp (v6)                ALLOW IN    Anywhere (v6)
# SSH
[ 7] 3000/tcp (v6)              ALLOW IN    Anywhere (v6)
# Grafana
[ 8] 9000/tcp (v6)              ALLOW IN    Anywhere (v6)
# eth2 p2p traffic
[ 9] 9090/tcp (v6)              ALLOW IN    Anywhere (v6)
# Prometheus
[10] 30303/tcp (v6)             ALLOW IN    Anywhere (v6)
# eth1 node

[ Optional but recommended ] Whitelisting (or permitting connections from a specific IP) can be setup via the following command.

sudo ufw allow from <your local daily laptop/pc>
# Example
# sudo ufw allow from 192.168.50.22

🎊 Port Forwarding Tip: You'll need to forward and open ports to your validator. Verify it's working with https://www.yougetsignal.com/tools/open-ports/ or https://canyouseeme.org/ .

📞 Verify Listening Ports

If you want to maintain a secure server, you should validate the listening network ports every once in a while. This will provide you essential information about your network.

sudo ss -tulpn
# Example output. Ensure the port numbers look right.
# Netid  State    Recv-Q  Send-Q    Local Address:Port   Peer Address:Port   Process
# tcp    LISTEN   0       128       127.0.0.1:5052       0.0.0.0:*           users:(("lighthouse",pid=12160,fd=22))
# tcp    LISTEN   0       128       127.0.0.1:5054       0.0.0.0:*           users:(("lighthouse",pid=12160,fd=23))
# tcp    LISTEN   0       1024      0.0.0.0:9000         0.0.0.0:*           users:(("lighthouse",pid=12160,fd=21))
# udp    UNCONN   0       0         *:30303              *:*                 users:(("geth",pid=22117,fd=158))
# tcp    LISTEN   0       4096      *:30303              *:*                 users:(("geth",pid=22117,fd=156))

Alternatively you can use netstat

sudo netstat -tulpn
# Example output. Ensure the port numbers look right.
# Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
# tcp        0      0 127.0.0.1:5052          0.0.0.0:*               LISTEN      12160/lighthouse
# tcp        0      0 127.0.0.1:5054          0.0.0.0:*               LISTEN      12160/lighthouse
# tcp        0      0 0.0.0.0:9000            0.0.0.0:*               LISTEN      12160/lighthouse
# tcp6       0      0 :::30303                :::*                    LISTEN      22117/geth
# udp6       0      0 :::30303                :::*                    LISTEN      22117/geth

👩‍🚀 Use system user accounts - Principle of Least Privilege [Advanced Users / Optional]

Recommended for Advanced Users Only

Principle of Least Privilege: Each eth2 process is assigned a system user account and runs under the least amount of privileges required in order to function. This best practice protects against a scenario where a vulnerability or exploit discovered in a specific process might enable access other system processes.

# creates system user account for eth1 service
sudo adduser --system --no-create-home eth1

# creates system user account for validator service
sudo adduser --system --no-create-home validator

# creates system user account for beacon-chain service
sudo adduser --system --no-create-home beacon-chain

# creates system user account for slasher
sudo adduser --system --no-create-home slasher

🔥 Caveats For Advanced Users

If you decide to use system user accounts, remember to replace the systemd unit files with the corresponding users.

# Example of beacon-chain.service unit file
User            = beacon-chain

Furthermore, ensure the correct file ownership is assigned to your system user account where applicable.

# Example of prysm validator's password file
sudo chown validator:validator -R $HOME/.eth2validators/validators-password.txt

✨ Additional validator node best practices

Networking	Assign static internal IPs to both your validator node and daily laptop/PC. This is useful in conjunction with ufw and Fail2ban's whitelisting feature. Typically, this can be configured in your router's settings. Consult your router's manual for instructions.
Power Outage	In case of power outage, you want your validator machine to restart as soon as power is available. In the BIOS settings, change the Restore on AC / Power Loss or After Power Loss setting to always on. Better yet, install an Uninterruptable Power Supply (UPS).
Clear the bash history	When pressing the up-arrow key, you can see prior commands which may contain sensitive data. To clear this, run the following: shred -u ~/.bash_history && touch ~/.bash_history

🤖 Start staking by building a validator

Congrats on completing the guide. ✨

🚀 References

How to Harden your Ubuntu 18.04 ServerMedium

Ubuntu system hardening guide for desktops and serversLinux Audit

How To Harden OpenSSH on Ubuntu 18.04 | DigitalOceanDigitalOcean

Configure SSH to use two-factor authentication | UbuntuUbuntu

How to Install and Configure Fail2ban on Ubuntu 20.04linuxize

https://gist.github.com/lokhman/cc716d2e2d373dd696b2d9264c0287a3#file-ubuntu-hardening-md

How to Harden Ubuntu Server 18.04 in 5 Easy StepsLifewire

The 50 Best Linux Hardening Security Tips: A Comprehensive ChecklistUbuntuPIT