Server Hardening

Never try on production servers without first testing it in a controlled lab on test equipment.

Hardening is the process of securing a system by reducing its attack surface. The attack surface is the sum of all the ways an attacker can interact with a system, including open ports, services, and vulnerabilities. By hardening Ubuntu, you can minimize the potential entry points for attackers and protect your system from various threats, such as malware, brute-force attacks, and unauthorized access.

Automated Security Hardening

It's advisable to audit the system before applying any hardening fixes. This will help you create a point of comparison.

Using Lynis

Lynis is a powerful, open-source security auditing and compliance tool designed for Unix-based systems like Linux, macOS, and BSD. Created and maintained by CISOfy, Lynis is widely used by system administrators, DevOps engineers, and security professionals to assess the security posture of servers in real time.

Lynis not only identifies security gaps but also provides actionable suggestions and warnings, helping us harden our systems effectively. It supports standards such as CIS benchmarks, ISO27001, HIPAA, and PCI-DSS, making it ideal for organizations with compliance requirements.

Step 1: Update

sudo apt update && sudo apt upgrade -y

Step 2: Install Lynis

sudo apt install lynis -y

Step 3: Verify Installation

lynis --version

Step 4: Run a basic scan

sudo lynis audit system

This inspects more than 200 system configurations and services like:

✅ Firewall settings

✅ Kernel parameters

✅ SSH, sudoers, and login policies

✅ File permissions

✅ Malware detection (via ClamAV)

✅ Logging and auditd configuration

Step 5: Analyze audit results

• After scanning, Lynis shows:

✅ Hardening index (0–100)

✅ Warnings (security issues)

✅ Suggestions (best practices)

• Log and summary files are saved at:

✅ /var/log/lynis.log

✅ /var/log/lynis-report.dat

Step 6: Automate weekly scans

Use cron to schedule:

sudo crontab -e

Add:

0 2 * * 0 /opt/lynis/lynis audit system --quiet >> /var/log/weekly-lynis.log

This runs every Sunday at 2 AM

Step 7: Use a custom audit profile (Advanced)

Create a profile for focused checks:

mkdir -p /etc/lynis/custom
cp /opt/lynis/default.prf /etc/lynis/custom/hardeningubuntu.prf

Edit it to include/exclude modules:

nano /etc/lynis/custom/hardeningubuntu.prf

Example:

skip-test=KRNL-5830  # skip IPv6 kernel test
enabled-test=AUTH-9222  # ensure sudo is protected

Run using the custom profile:

sudo ./lynis audit system --profile /etc/lynis/custom/hardeningubuntu.prf

Step 8: Export and parse audit data

You can extract specific security events:

grep "^warning" /var/log/lynis-report.dat
grep "^suggestion" /var/log/lynis-report.dat

Hardening the System

This is an editable version of a script that executes actions for CIS Compliance. This script should be reviewed and updated periodically with the latest security compliance recommendations.

Never try a new automation script on production servers without first testing it in a controlled lab on test equipment

Run the following script:

22KB

hardening-ubuntu-2404-v2.sh

Open

Perform gap analysis and audit again.

GAP analysis is a methodology used to evaluate the differences between the initial state of an organization's information systems and the level of compliance required by the standard it wants to comply with.

Manual Security Hardening

Follow these steps to perform manual hardening:

Initial Setup

✅ Perform an audit with Lynis

✅ Review the audit results.

✅ Review, edit, and run the hardening script we attached in the previous session. You can adjust the following recommended hardening parameters in the script listed below:

Secure SSH Access

✅ Disable the root login.

✅ Disable it by setting the PermitRootLogin value to no in the etc/ssh/sshd_config file.

✅ Change the default SSH port.

✅ Uncomment and replace port 22 in etc/ssh/sshd_config

✅ Replace password authentication with SSH keys

✅ Use key-based authentication only

✅ Create a new SSH key pair

✅ Disable password authentication by setting the PasswordAuthentication value to no in the etc/ssh/sshd_config file.

✅ Restart sshd to apply the changes.

Enable AppArmor

Check if AppArmor is active and enabled

sudo systemctl status apparmor

Activate and enable AppArmor

sudo systemctl enable apparmor
sudo systemctl start apparmor

Check the currently active profiles

AppArmor profiles support two different modes of operation: enforce and complain. While enforce mode prevents applications from taking restricted actions, complain mode only logs those actions.

sudo apparmor_status

Enable the Firewall

Configure the firewall to allow only permit connections. Allow SSH and Solana validator ports:

Port	Service
8000	Gossip Solana
8001	Gossip alternative Solana
8899	RPC public Solana
8900	WebSocket RPC Solana
9000	TPU (Transaction Processing Unit) Solana
7000	Retransmission Solana
10000	Retransmission alternative Solana
8008	HTTP proxy o debug service
8015	cfg-cloud service
8020	intu-ec-svcdisc custom

Start the firewall and set it to load at boot

sudo ufw enable

Enable firewall logging

sudo ufw logging on

Update and Upgrade

# Update the package information 
sudo apt update
# Simulate an upgrade of all packages
sudo apt-get upgrade -s
# If you’re satisfied with the simulation output, you can proceed to upgrade all packages.
sudo apt-get upgrade

If not, you can upgrade any individual packages one by one. Remember to replace $packagename with the name of each package.

sudo apt-get install --only-upgrade $packagename

Remove Unused Packages

sudo apt autoremove

Find and remove unused packages with Deborphan

sudo apt install deborphan

List the unused packages

deborphan

Remove the unused packages

apt-get remove $packagename

Use strong passwords

Use pwgen to generate a strong password

sudo apt install pwgen

Generate a list of passwords using the -ys flag, where y means include symbols, and s is used to generate a highly secure password string.

pwgen -ys 20 1

Set a password expiration policy

Use the etc/login.defs file to set a shorter password expiration policy, such as 30 to 90 days.

• PASS_MAX_DAYS is the number of days after which a password will expire.

• PASS_MIN_DAYS is the number of days that need to pass before a password can be changed.

• PASS_WARN_AGE is the number of days warnings will be shown on log in before the password expires. This feature doesn’t extend the PASS_MAX_DAYS expiration.

Apply the new policy to existing users

sudo chage -l $username
sudo chage -M $days $username

Configuring Fail2Ban to protect SSH

sudo apt install fail2ban
sudo systemctl enable fail2ban
sudo systemctl start fail2ban

Now add your IP to the ignoreip list and uncomment the line and configure how the system should treat suspicious IPs.

• bantime defines how long an IP will be blocked.

• maxretry is how many times an IP can fail to log in before getting blocked.

• findtime is the time period after which the maxretry counter is reset.

Open the file “defaults-debian.conf ”

sudo nano /etc/fail2ban/jail.d/defaults-debian.conf 

[DEFAULT]
banaction = nftables
banaction_allports = nftables[type=allports]
backend = systemd

[sshd]
enabled = true
port = ssh
maxretry = 3
findtime = 300 
bantime = 3600
ignoreip = 127.0.0.1

Restart and check the service

sudo systemctl restart fail2ban
sudo systemctl status fail2ban

Monitoring and testing

sudo fail2ban-client status sshd

Unban manually:

sudo fail2ban-client unban --all
sudo fail2ban-client unban <ip-address>

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What’s Next?

Network Security Hardening, configure a Bastion host or use the menu on the left to explore the rest of the documentation. If you’re just experimenting, localnet is all you need. If you’re going live, follow the full setup under Validator Operations.