Change SSH Port from 22 to 61613

30 minutes
  • 4 Learning Objectives

About this Hands-on Lab

After you start any instance with public access, automated scripts will find you almost immediately and start conducting all sorts of scans and probing. There is no real way to completely stop this. You can confirm this is happening by looking at the log files of any public instance you create. However, we don’t need to make it easy for them. A standard scan will usually check for known standardized ports associated with known services. For example, SSH by default runs on port 22 and is the first port any script will check for an SSH service. Now, if we configure SSH service to run on port 61613, the scan script will need to make a broad port sweep to find our SSH service. This is extremely taxing in terms of bandwidth for the attacker, and generally scripts will not check for these ports. That is why it is very important for us to change the port at which SSH operates from 22 to something that is not standardized, making it much more difficult for any one script to find our SSH service.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Open `/etc/ssh/sshd_config`, Uncomment the `Port` Variable, and Change the Value from 22 to 61613

Note: Use a local terminal app with ssh support for this lab. The Instant Terminal can not be used for this specific lab.

  1. Open configuration file:

    sudo vim /etc/ssh/sshd_config
    1. Change the value of Port:

      Port 61613
    2. Save and close:

      ESC
      :wq
      ENTER
Open Port 61613 with firewalld
  1. Open the port with firewalld:

    sudo firewall-cmd --permanent --add-port=61613/tcp
    1. Reload to apply the rules:
    sudo firewall-cmd --reload
Configure SELinux to Allow Connections on Port 61613 for SSH
sudo semanage port -a -t ssh_port_t -p tcp 61613 
Restart SSH, Log Out and Back in on Port 61613, and Close Port 22 with firewalld
  1. Restart SSH:

    sudo systemctl restart sshd
  2. Log out:

    exit
  3. Log in on port 61613:

    ssh cloud_user@<Server_IP_Address> -p 61613
  4. Close port 22 with firewalld:

    sudo firewall-cmd --permanent --remove-port=22/tcp
    sudo firewall-cmd --reload

Additional Resources

Generally speaking, every time you have a front-facing server, that server in all likelihood will be probed by a large number of automated scans. One of the first things these scripts check is port 22 because it is a well-known port, and SSH usually works on this port. However, we have no reason to make their lives easier.

By changing the port of SSH from 22 to something highly unusual — like, let's say, port 61613 — a large number of those automated scans will fail to detect there is in fact SSH running on the server, as they do not expect this.

But simply changing the default port and not doing anything else is a sure way of locking yourself out of the server. So we need to configure SELinux to allow connections on port 61613 for SSH, and we need to instruct the firewall to allow traffic on port 61613. Furthermore, we can do some housekeeping and close port 22.

Note: Use a local terminal app with ssh support for this lab. The Instant Terminal can not be used for this specific lab.

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