Eight ways to protect SSH access on your system Enable Sysadmin

I’m going to take you through eight steps to better help you secure the SSH service on your network. It allows us to connect to and from Linux devices, Unix servers, network appliances, and sometimes even Windows boxes.

It is possible to directly forward ports for single jumps instead of forwarding the agent. This has the advantage of never exposing your agent to the servers you’re connecting to. OpenSSH 7.3 onwards allow users to jump through several hosts in a rather automated fashion. It has full support for scp and sftp commands as well as regular ssh. If you have a file containing known_hosts using RSA or ECDSA host key algorithm and the server now supports ed25519 for example, you will get a warning that the host key has changed and will be unable to connect. # Password based logins are disabled – only public key based logins are allowed.

The What, Why & How of SSH Protocol

It is also embedded inside many file transfer and systems management solutions. We can also make our SSH server secure by setting a specific number of password tries.

Kaji malwaretargets IoT devices that have left their SSH port exposed on the internet. According to the researchers who discovered this malware, once it gains access to a device’s root account, Kaiji will use the device in three ways. Second, to carry out more SSH brute-force attacks against other devices. Third, to steal any local SSH keys and spread to other devices the root account has managed in the past. During the connection setup, the client and server negotiate and agree upon the symmetric encryption algorithm to be used for their communication and generate the encryption key to be used. The server’s public key is saved in the client’s known hosts file. The above list is a summary of SSH risks that exist in traditional IT, as well as cloud environments.

How the SSH Protocol Works

If you want to prevent root from logging in at all, replace “prohibit-password” with “no”. Scroll through the file until you see the line that starts with “#PermitRootLogin prohibit-password” Remove the hash # from the start of the line. Note that MaxAuthTries number seemed to be one more than the number of tries the user was permitted. Hardening and locking down a Linux or Unix-like operating system can get very involved, very quickly. What we’re presenting here is a set of easy to implement steps that will improve the security of your computer without the need for third-party applications and without digging through your firewall.

• Even if the key gives non-root access, local privilege escalation vulnerabilities can often result in the attacker gaining root access.
• Ylonen still works on topics related to Secure Shell, particularly around key management, as well as broader cybersecurity topics.
• This will automatically forward the SSH connection over ssh.mozilla.com when you connect to a mozilla.com SSH server.
• Each new usage (different service, different script called, etc.) should use a new, different key.
• Scroll through the file until you see the line that starts with “#PermitRootLogin prohibit-password” Remove the hash # from the start of the line.

In 1995, Tatu Ylönen, a researcher at Helsinki University of Technology, Finland, designed the first version of the protocol (now called SSH-1) prompted by a password-sniffing attack at his university network. The goal of SSH was to replace the earlier rlogin, TELNET, FTP and rsh protocols, which did not provide strong authentication nor guarantee confidentiality. Ylönen released his implementation as freeware in July 1995, and the tool quickly gained in popularity. Towards the end of 1995, the SSH user base had grown to 20,000 users in fifty countries. The IANA has assigned TCP port 22, UDP port 22 and SCTP port 22 for this protocol. IANA had listed the standard TCP port 22 for SSH servers as one of the well-known ports as early as 2001.

Version 1.99

The Secure Shell Protocol is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. When you make a connection request, the remote computer uses its copy of your public key to create an encrypted message that is sent back to your computer. Because it was encrypted with your public key, your computer can unencrypt it with your private key. The public key is installed on the servers you wish to connect to.

• Better security, for example, comes through Diffie–Hellman key exchange and strong integrity checking via message authentication codes.
• They are commonly used in scripts, backup systems, configuration management tools, and by developers and sysadmins.
• The protocol works in the client-server model, which means that the connection is established by the SSH client connecting to the SSH server.
• Depending on the computing needs, the firewall can also inspect traffic within a private network, significantly improving the server’s security.
• The private, or the identification key, will be saved as id_rsa and the corresponding public key as id_rsa.pub.

We can set a limit for password tries by changing ssh_config file. As described earlier, by default SSH uses Port 22 for communication. It is much easier for hackers to hack your data if they know which port is being used for communication.

SSH-1

The SSH client drives the connection setup process and uses public key cryptography to verify the identity of the SSH server. After the setup phase the SSH protocol uses strong symmetric encryption and hashing algorithms to ensure the privacy and integrity of the data that is exchanged between the client and server.

Ylonen still works on topics related to Secure Shell, particularly around key management, as well as broader cybersecurity topics. Machine keys do not play well with multi-factor authentication as there is no human interaction. Restrict privileges of the account (i.e. no root or “sudoer” machine account). The keys must be accessible only by the admin user and/or the system user requiring access. Use SSH forwarding or SSH tunneling if you need to jump between hosts.

Teleport Use Cases

The open source Windows program WinSCP provides similar file management capability using PuTTY as a back-end. Both WinSCP and PuTTY are available packaged to run directly off a USB drive, without requiring installation on the client machine.

• Dating back to the days where encryption wasn’t available for all protocols, SSH features the ability to forward traffic sent to a local port on an SSH client.
• You may also implement port knocking so that it becomes much harder to detect open SSH ports.
• Congratulations, you have successfully disabled the option to log in through SSH using account passwords.
• A firewall’s primary job is to inspect incoming and outgoing traffic using predefined rules.
• The SSH client drives the connection setup process and uses public key cryptography to verify the identity of the SSH server.

If you are using a non-standard port and someone still tries to access your server, it probably means that your server is specifically being targeted and that the alarm is not coming from a scripted attack. SSH daemon can take a break since it will not get connection requests from scripted attacks. Server load is reduced, and the log file stays clean saving you time in reviewing it. Use a text editor of your choice to edit the sshd configuration file located in the etc/ssh/ directory. If you have never used a text editor within the terminal, it is recommended to use Nano. Otherwise, use vi or vim since they are the most commonly used editors today. We advise you to back up the original file before you make any changes.