SSH Security Best Practices: 10 Ways To Secure Your Linux Servers

Contents

1. Introduction
2. Best Practice #1
3. Best Practice #2
4. Best Practice #3
5. Best Practice #4
6. Best Practice #5
7. Best Practice #6
8. Best Practice #7
9. Best Practice #8
10. Best Practice #9
11. Best Practice #10
12. Conclusion

Introduction Server security is no longer something businesses can afford to treat as an afterthought. Every application, database, API, and cloud infrastructure depends on servers that must be properly secured against unauthorised access. And the events of October 2026 are a timely reminder of just how serious the risks have become. Within a single week, several significant security incidents and vulnerabilities highlighted the growing threats facing modern infrastructure.

On October 21, the PHP development team released emergency security updates addressing two critical vulnerabilities, that can allow unauthenticated attackers to execute arbitrary code remotely on affected systems. These vulnerabilities were collectively referred to as PHP2Shell

Around the same time, Railway disclosed a security incident involving unauthorised access to internal systems.

Then came Node2Shell, a critical vulnerability affecting the Brotli decoder used by Node.js. The vulnerability can allow attackers supplying malicious Brotli-compressed input to trigger memory corruption, potentially resulting in remote code execution, information disclosure, or denial of service.

These incidents highlight an important reality, i.e securing an application is not enough if the underlying infrastructure remains exposed.

One of the most important components of Linux server security is Secure Shell (SSH). SSH provides administrators and developers with remote access to Linux servers. However, when poorly configured, it can become an entry point for attackers attempting to gain access to production environments, Hence implementing proper SSH security controls should be a priority.

Let's explore 10 SSH security best practices every system administrator and DevOps engineer should implement.

Best Practice #1 Disable SSH Password Authentication One of the first things you should do when securing a Linux server is disable password-based SSH authentication and instead use SSH key-based authentication. This provides a stronger alternative, instead of entering a password every time you connect, your local machine uses a private key to authenticate against a corresponding public key stored on the server.

Password authentication is convenient, but it introduces several security risks. Attackers routinely scan publicly accessible servers and attempt to gain access using common usernames and passwords. These attacks, commonly known as brute-force attacks, involve trying thousands of possible password combinations until a valid credential is discovered.

Best Practice #2 Disable Root SSH Login The root account has unrestricted administrative privileges on a Linux server. Allowing direct SSH access to root increases the consequences of compromised credentials. If an attacker successfully authenticates as root, they immediately gain administrative control without needing to escalate privileges. A better approach is to create a dedicated administrative user and grant elevated privileges through sudo.

Best Practice #3 Change the Default SSH Port By default, SSH listens on TCP port 22. Because this port is widely known, automated scanners frequently target it when searching for publicly accessible SSH servers.

Changing the default port can reduce noise from automated scans and decrease the number of basic brute-force attempts appearing in your authentication logs.

Best Practice #4 Restrict SSH Access to Trusted IP Addresses Not everyone should be able to connect to your production servers. If your organisation has a fixed office IP address, VPN, or dedicated administrative network, consider restricting SSH access to those trusted sources.

Best Practice #5 Disable Unnecessary SSH Features SSH provides several useful capabilities beyond remote shell access. These include:

• TCP forwarding.
• X11 forwarding.
• Agent forwarding.
• Tunnelling.
• Port forwarding.

While these features are useful, they can also introduce additional attack surfaces. If your servers do not require these capabilities, disable them.

Best Practice #6 Install Fail2Ban to Reduce Brute-Force Attacks Even after disabling password authentication, publicly exposed SSH services continue to receive automated connection attempts. Fail2Ban helps reduce this activity by monitoring authentication logs and temporarily banning IP addresses that generate repeated failed authentication attempts.

Best Practice #7 Keep OpenSSH and Your Linux Server Updated One of the most overlooked aspects of infrastructure security is keeping software up to date. Security vulnerabilities are regularly discovered in operating systems, SSH implementations, cryptographic libraries, and other system components.

The October 2026 PHP2Shell and Node2Shell disclosures demonstrate why organisations must take vulnerability management seriously. Although these vulnerabilities are not SSH vulnerabilities, they illustrate how an exposed production service can become an entry point for attackers. A compromised application may provide opportunities for attackers to access configuration files, environment variables, SSH keys, or other sensitive resources.

Keep your Ubuntu server updated

Best Practice #8 Protect SSH Private Keys Your SSH private key is effectively an authentication credential. Anyone who obtains an unprotected private key may be able to access the systems associated with that key. Never store private keys in publicly accessible repositories, shared folders, or application directories.

Best Practice #9 Monitor SSH Authentication Logs Security controls are only useful when you can identify suspicious activity. Regularly monitor SSH authentication logs for:

• Repeated failed login attempts.
• Login attempts from unfamiliar IP addresses.
• Successful logins outside normal working hours.
• Unexpected root login attempts.
• New SSH public keys.
• Changes to SSH configuration.
• Unexpected user account creation.

Best Practice #10 Regularly Audit Your SSH Configuration SSH security should not be a one-time configuration exercise. Over time, new users are created, old credentials remain active, configuration changes are introduced, and infrastructure evolves. Regular security audits help identify configuration weaknesses before attackers exploit them.

Conclusion The security incidents and vulnerabilities disclosed in October 2026 should serve as a reminder that infrastructure security requires continuous attention.

The PHP2Shell vulnerabilities demonstrated how a vulnerable application runtime could expose systems to unauthenticated remote code execution.

The Railway incident highlighted the risks associated with unauthorised access to internal infrastructure and the potential exposure of customer credentials.

Node2Shell demonstrated how a vulnerability in a widely used compression component could potentially become an entry point for remote code execution.

These are different security problems, but they share an important lesson, which is: weaknesses in one layer of your infrastructure can have consequences far beyond that individual component.

SSH remains one of the most important tools for managing Linux infrastructure. Properly configured, it provides a secure and reliable way to administer production environments.

Your production environment is only as secure as the controls protecting access to it.