Locking Down Remote Access to Linux

30 minutes
  • 2 Learning Objectives

About this Hands-on Lab

In this lab, we will look at how to lock down remote access to a Linux host. We will accomplish this by restricting all remote logins for the `root` account as well as restricting SSH access based on account names.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Prevent remote logins from using the `root` account.
  1. In order to prevent remote logins from using the root account, we’ll need to edit the /etc/passwd file. Run the following command:

    sudo vipw 
    • select #2 for nano (easiest)
  2. Next, edit the line that starts with root and replace /bin/bash with /sbin/nologin.

  3. Save and exit the /etc/passwd file.

Permit only the `cloud_user` account to connect to the host via SSH.
  1. In order to filter SSH access and only permit the cloud_user account to access the host via SSH, we’ll need to edit the sshd_config file with the following command:

    sudo nano /etc/ssh/sshd_config
  2. Add the following line to the file just under the second line of the file:

    AllowUsers cloud_user

    Note: You can also restrict user access by source hostname, IP address, or subnet, like:

    AllowUsers cloud_user@10.0.0.0/24
    AllowUsers Jhalpert@james.host.int
    AllowUsers mscott@192.168.55.10
  3. Now, restart the ssh service with the following command:

    sudo service ssh restart

Additional Resources

You have been asked to lock down remote access to a new Linux server. Your supervisor has requested you prevent all remote logins for the root account and only permit remote SSH access for the cloud_user account.

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