Objective

Harden a Linux virtual machine (VM) deployed in AWS against common threats by applying security best practices. This checkpoint demonstrates how to protect cloud-hosted Linux systems through SSH hardening, filesystem security, patch management, firewall configuration, and user privilege separation.

Implementation

• SSH Hardening
  • Edit /etc/ssh/sshd_config:

# Disable root login:

PermitRootLogin no

# Disable password authentication

PasswordAuthentication no

# Restart SSH service:

sudo systemctl restart ssh

• Filesystem Security

# Restrict access to sensitive files:

sudo chmod 640 /etc/shadow
sudo chown root:shadow /etc/shadow

# Ensures only privileged processes can read password hashes.

• Patch Management

# Enable automatic security updates:

sudo apt install unattended-upgrades
sudo dpkg-reconfigure --priority=low unattended-upgrades

# Keeps the system updated with the latest patches.

• Firewall Setup

# Enable UFW and allow only essential ports:bash

sudo ufw enable
sudo ufw allow 22/tcp
sudo ufw allow 80/tcp
sudo ufw allow 443/tcp

# Blocks all other traffic by default.

• Create Non‑Root User

# Add a dedicated user for administration:

sudo adduser engineer
sudo usermod -aG sudo engineer

# Reduces risk by avoiding direct root access.

Deliverable

• Security Checklist documenting:
  • SSH hardening steps.
  • Filesystem permission changes.
  • Patch management configuration.
  • Firewall rules.
  • Non-root user creation.

Checkpoint

Learners reflect on:

• Which hardening step most improves production readiness.
• Example reflections:
  • SSH hardening prevents brute-force root login attempts.
  • Patch management ensures ongoing protection against vulnerabilities.
  • Firewall rules minimize attack surface.

Hackers Notebook

Securing a Linux VM in AWS requires layered defense:

• SSH hardening eliminates weak authentication vectors.
• Filesystem security protects sensitive credentials from unauthorized access.
• Patch management ensures vulnerabilities are addressed promptly.
• Firewall configuration enforces strict traffic control.
• Non-root user creation enforces the principle of least privilege.

Together, these measures form a baseline security posture for cloud-hosted Linux systems, aligning with industry best practices for production readiness.