ANSWER-FIRST ARCHITECTURAL SUMMARY

To secure fresh VPS instances against brute-force and SYN-flood attacks, disable password authentication by implementing Ed25519 SSH keys, configure Fail2ban with systemd-journald integration for monitoring and banning malicious IPs, and apply optimized sysctl parameters for enhanced network security. Key commands include `ssh-keygen -t ed25519`, `systemctl enable fail2ban`, and editing `/etc/sysctl.conf` for TCP settings. This guide is tailored for senior systems and DevOps engineers seeking robust security measures.

Prerequisites & Environment

Familiarity with Linux command line
Basic understanding of SSH and networking
Access to a fresh Ubuntu 24.04 VPS instance

Automated Hardening Blueprint for Fresh VPS Instances#

Introduction#

Fresh VPS instances are often targeted by automated botnet attacks within minutes of provisioning. This guide outlines a systematic approach to hardening your Ubuntu 24.04 server by disabling password authentication, configuring Fail2ban, and optimizing network parameters.

1. Disable Password Authentication#

To enhance security, disable password authentication in favor of Ed25519 SSH keys.

1.1 Generate Ed25519 SSH Keys#

Use the following command to generate a new SSH key pair:

BASH

ssh-keygen -t ed25519 -C "your_email@example.com"

This command creates a public/private key pair in `~/.ssh/`. Ensure to add the public key to the `~/.ssh/authorized_keys` file on your server.

1.2 Update SSH Configuration#

Edit the SSH configuration file:

BASH

sudo nano /etc/ssh/sshd_config

Change or add the following lines:

PLAINTEXT

PermitRootLogin no
PasswordAuthentication no
ChallengeResponseAuthentication no

Restart the SSH service:

BASH

sudo systemctl restart ssh

2. Configure Fail2ban with systemd-journald#

Fail2ban helps protect your server from malicious login attempts by banning IP addresses that show malicious signs.

2.1 Install Fail2ban#

Install Fail2ban using the package manager:

BASH

sudo apt update
sudo apt install fail2ban

2.2 Configure Fail2ban#

Create a new configuration file for SSH protection:

BASH

sudo nano /etc/fail2ban/jail.local

Add the following configuration:

PLAINTEXT

[sshd]
enabled = true
filter = sshd
action = systemd-journal[name=sshd, dest=/var/log/auth.log]
logpath = /var/log/auth.log
maxretry = 3
bantime = 3600

Enable and start the Fail2ban service:

BASH

sudo systemctl enable fail2ban
sudo systemctl start fail2ban

3. Optimize sysctl Parameters#

Adjust Linux kernel parameters to improve network security and performance.

3.1 Edit sysctl Configuration#

Open the sysctl configuration file:

BASH

sudo nano /etc/sysctl.conf

Add or modify the following parameters:

PLAINTEXT

# Enable SYN cookies
net.ipv4.tcp_syncookies = 1

# Protect against IP spoofing
net.ipv4.conf.all.rp_filter = 1

# Increase TCP buffer sizes
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216

Apply the changes:

BASH

sudo sysctl -p

Conclusion#

By following this guide, you can significantly enhance the security of your fresh Ubuntu 24.04 VPS. Regularly review your security settings and stay updated on best practices to maintain a robust defense against evolving threats.

[!NOTE] Always back up your configuration files before making changes.

[!WARNING] Ensure you have console access to your VPS in case of misconfiguration.

Written by Alex Carneiro

Founder & Systems Architect at PerMesh. Focused on clean production engineering, automated pipelines, and fast web architectures.