SSH (Secure Shell) is a fundamental tool for securely accessing remote servers, but its security depends heavily on proper configuration. If you’re managing a server, implementing robust security measures for SSH is essential to protect your system from unauthorized access and potential breaches. Here’s a comprehensive guide to securing your SSH server.

Use SSH Keys Instead of Passwords

Passwords can be a weak link in security, especially if they are not complex or are vulnerable to brute-force attacks. SSH keys are a more secure method of authentication.

• Generate an SSH Key Pair: Create a key pair on your local machine using ssh-keygen. Choose a strong encryption algorithm such as ed25519 for generating the keys.
• Deploy the Public Key: Copy your public key to the server using ssh-copy-id. This allows you to log in without a password.

Configuration: In your /etc/ssh/sshd_config file, disable password authentication:

PasswordAuthentication no
PubkeyAuthentication yes

Disable Root Login

Allowing direct root login can be risky as it exposes the highest level of access to potential attackers.

Configuration: To disable root login, edit /etc/ssh/sshd_config:

PermitRootLogin no

Change the Default Port

The default SSH port is 22, which is well-known and often targeted by automated attacks. Changing it to a non-standard port can reduce the number of automated attacks.

Configuration: Change the SSH port in /etc/ssh/sshd_config:

Port 2222

Restrict User Access

Limiting SSH access to specific users or groups reduces the risk of unauthorized access.

Configuration: Specify allowed users or groups in /etc/ssh/sshd_config:

AllowUsers user1 user2
# or
AllowGroups sshgroup

Enforce Strong Encryption

Using strong encryption algorithms and key exchange methods ensures that your data remains confidential and secure.

Configuration: Set strong ciphers, MACs, and key exchange algorithms in /etc/ssh/sshd_config:

Ciphers aes256-ctr,aes192-ctr,aes128-ctr
MACs hmac-sha2-256,hmac-sha2-512
KexAlgorithms [email protected]

Set Idle Timeouts and Limit Attempts

Configuring idle timeouts and limiting the number of authentication attempts helps mitigate the risk of brute-force attacks and unauthorized access.

Configuration: In /etc/ssh/sshd_config, set:

ClientAliveInterval 300
ClientAliveCountMax 0
MaxAuthTries 3
MaxSessions 2

Monitor and Log Connection Attempts

Logging SSH activities allows you to monitor for suspicious behavior and take action if necessary.

Configuration: Increase the verbosity of logging in /etc/ssh/sshd_config:

LogLevel VERBOSE

Regularly Review Logs: Check /var/log/auth.log to monitor for unusual activity.

Conclusion

Implementing these best practices will significantly enhance the security of your SSH server, protecting it from unauthorized access and potential breaches. Regularly review and update your security measures to keep up with evolving threats.

Stay secure and ensure your server is protected with these essential SSH security configurations.