Security Best Practices for your ETH staking validator node

Quick steps to secure your node.

Completing this guide will provide a solid baseline to protect and secure your staking node.

πŸ€– Pre-requisites

  • Ubuntu Server or Ubuntu Desktop installed on a local computer. Bonus points for increasing decentralization of Ethereum and not relying on cloud providers.

  • a SSH client or terminal window access

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

πŸ§™β€β™‚οΈ Mandatory: Create a non-root user with sudo privileges

If you're using Ubuntu Desktop then you're likely currently on your staking node. Simply open a terminal window from anywhere by typing Ctrl+Alt+T.

Otherwise, begin by connecting to Ubuntu Server with your SSH client.

ssh username@staking.node.ip.address

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

πŸ” Mandatory: Disable SSH password Authentication and Use SSH Keys only

If you're using Ubuntu Desktop locally, you can skip this section.

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.

ssh-keygen -t ed25519

Your SSH key pair is stored in your home directory. For example, if your keyname was mySSHkey, then your private SSH key is mySSHkey and your public SSH key is mySSHkey.pub

IMPORTANT: Make multiple backup copies of your private SSH key file to external storage, such as a USB backup key, for recovery purposes.

Verify the contents of your private SSH key file before moving on.

cat <keyname>

It should look similar to this example.

-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
QyNTUxOQAAACBAblzWLb7/0o62FZf9YjLPCV4qFhbqiSH3TBvZXBiYNgAAAJCWunkulrp5
LgAAAAtzc2gtZWQyNTUxOQAAACBAblzWLb7/0o62FZf9YjLPCV4qFhbqiSH3TBvZXBiYNg
AAAEAxT+yCmifGWgbFnkauf0HyOAJANhYY5EElEX8fI+M4B0BuXNYtvv/SjrYVl/1iMs8J
XioWFuqJIfdMG9lcGJg2AAAACWV0aDJAZXRoMgECAwQ=
-----END OPENSSH PRIVATE KEY-----

Transfer the public key to your remote node. Replace <keyname.pub> appropriately.

ssh-copy-id -i $HOME/<keyname.pub> ethereum@staking.node.ip.address

Login with your new ethereum user

ssh ethereum@staking.node.ip.address

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

sudo nano /etc/ssh/sshd_config

Locate PubkeyAuthentication and update to yes. Delete the #, if needed.

PubkeyAuthentication yes

Locate PasswordAuthentication and 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.

Port <your random port number>

A valid random port # ranges from 1024 thru 49141.

Check that the port is not already used by other services. Replace <port> with your random port #.

sudo ss -ntlp | grep :<port>

Empty response means the port is good.

A response with red numbers means the port is already used. Choose another port.

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

ssh ethereum@staking.node.ip.address

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 <staking.node.ip.address>
  Port <custom random port number>

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

πŸ€– Mandatory: 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

Reboot your system to enable the upgrades.

sudo reboot

🧱 Mandatory: 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.

  • If you used a custom random SSH port, replace "22" with your actual port #.

# By default, deny all incoming and outgoing traffic
sudo ufw default deny incoming
sudo ufw default allow outgoing
# Allow ssh access
sudo ufw allow 22/tcp
# Allow consensus client port
sudo ufw allow 9000
# Allow execution client port
sudo ufw allow 30303
# Enable firewall
sudo ufw enable

Confirm the settings are in effect.

sudo ufw status numbered

Example of properly configured ufw status for Lighthouse.

     To                         Action      From
     --                         ------      ----
[ 1] 22/tcp                     ALLOW IN    Anywhere
[ 2] 9000                       ALLOW IN    Anywhere
[ 3] 30303                      ALLOW IN    Anywhere
[ 4] 22/tcp (v6)                ALLOW IN    Anywhere (v6)
[ 5] 9000 (v6)                  ALLOW IN    Anywhere (v6)
[ 6] 30303 (v6)                 ALLOW IN    Anywhere (v6)

Port Forwarding Tip: You'll need to forward and open ports to your validator.

Verify port forwarding is working with

As an example, for Lighthouse, you would verify ports 9000 and 30303 are reachable.

For advice on configuring port forwarding with routers, refer to this general port forwarding guide.

[ Optional ] Whitelisting, which means 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

⛓️ Mandatory: 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.

πŸ”₯ 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

🐻 Optional: 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

πŸ› οΈ Optional: Setup Two Factor Authentication for SSH

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 β€œtime-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.

🧩 Optional: 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

πŸ‘©β€πŸš€ Optional: Use system user accounts - Principle of Least Privilege [Advanced Users]

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

πŸ”₯ 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

πŸš€ References

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

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