SSH brute force attacks remain one of the most common threats facing servers connected to the internet. Attackers use automated tools to try thousands of username and password combinations, hoping to gain unauthorized access. Protecting your SSH service requires a multi-layered approach combining configuration hardening and active monitoring.

The first line of defense is disabling password authentication entirely and using SSH key-based authentication instead. SSH keys use cryptographic pairs that are virtually impossible to brute force. Additionally, changing the default SSH port from 22 to a non-standard port reduces automated scan visibility, though security through obscurity should never be your only protection.

Implementing fail2ban or similar intrusion prevention systems is essential. These tools monitor authentication logs and automatically block IP addresses that show signs of brute force activity. A typical configuration might block an IP for 30 minutes after 5 failed login attempts, with increasing ban durations for repeat offenders.

Rate limiting at the firewall level provides another protective layer. Using iptables or nftables, administrators can limit the number of new SSH connections per minute from any single IP address. This slows down brute force attempts significantly without impacting legitimate users.

Two-factor authentication adds yet another security dimension to SSH access. Tools like Google Authenticator or hardware tokens ensure that even if credentials are compromised, attackers cannot access the system without the second factor. Combined with strict user account policies and regular security audits, these measures create a robust defense against SSH-based attacks.