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Introduction

Outlined here are the steps to ensure your Ubuntu server has basic security.

Note

A disclaimer here. These are basic steps to securing the box. An actual hardening guide is something that I might write about in the future as a separate article.

Allow staff Group to sudo

Instead use account names associated with a user. For this example, I will be designating adminstrative users under the staff group. To see the list of groups available to you use the command, cat /etc/group.

The staff group by default does not normally have sudo access. To grant sudo access to the staff group,

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visudo

visudo launches your default editor to a special file. Add the following to the bottom of the file,

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# Members of this group may gain root privileges
%staff ALL=(ALL) ALL

Create Catch-All serveradmin user

The purpose of serveradmin is the catch-all place to setup things like scripts. It may also, depending on requirements for your organization be used to manually setup software like application servers.

Tip

Further along these lines, in a more security sensitive environment rather than just one serveradmin, we could setup distinct accounts for running a manual setup of tomcat, manual setup of postgressql etc.

Also, the serveradmin account is limited in that it can not use sudo. If an attacker compromises the application, sudo is still out of reach.

Add the user and assign a password to that user,

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sudo addgroup --gid 3000 serveradmin
sudo useradd -d /home/serveradmin -m -g serveradmin -u 3000 -c "Admin catch-all" -s /bin/bash serveradmin
sudo passwd serveradmin

Create Staff Users

We will also create staff users associated with the built in staff group so we know who is working on the machine. As a policy, our team requires that unless absolutely necessary, staff log in as their own account and then su to serveradmin or use sudo for maintenance work. That way we can have a trail of who does what.

sudo useradd -d /home/bhitch -m -g staff -u 2002 -c "Support Bryan Hitch" -s /bin/bash bhitch
sudo useradd -d /home/jcassaday -m -g staff -u 2002 -c "Support John Cassaday" -s /bin/bash jcassaday
sudo useradd -d /home/wellis -m -g staff -u 2001 -c "Support Warren Ellis" -s /bin/bash wellis

Notice the -u which set's the user's GUIDs. We found it essential to standardize on the GUID of the accounts across all our systems consistently. Not doing so causes problems when it comes to cloning systems or moving programs across different environments. As a practice, we use the following GUID's ranges,

  • Staff between 2000-2499
  • Guest Staff Users 2500-2999
  • Custom services 3000 - 3999

Additionally, we use the following group GUID ranges,

  • Custom services 3000 - 3999
  • I further broke up my custom services with Web Groups for website management - 3100-3199

Finally we add to the Staff users the following groups,

  • serveradmin - so staff users can work with manually setup apps
  • adm - so staff can view logs in apps setup using the sudo command
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sudo usermod -a -G serveradmin,adm bhitch
sudo usermod -a -G serveradmin,adm jcassaday
sudo usermod -a -G serveradmin,adm wellis


Warning

At this point it is important to logout and log in with your staff account to continue your work.

Disable Direct Login as Root Through SSH

Normally having permit root login in ssh in Ubuntu is not a security issue. Root is simply disabled in the OS. This is a hosted Ubuntu only step where often the root account is enabled. This is dangerous because there are attackers out there looking for Unix/Linux boxes and trying to login via ssh using the username root and then a list of common passwords.

Note

I do not going down the route of disabling the root account as this might break the hosted Ubuntu setup. For example, Slice's or Rackspace special terminal console login might stop working. In any event, the vector of attack is SSH login. To prevent users from using root, well don't provide the root password and provide sudo privileged accounts as shown in this article.


Connect to SSH as a staff user and edit sshd_config,

sudo nano /etc/ssh/sshd_config

Search for the line "PermitRootLogin yes" and change to "PermitRootLogin no". You can still issue su to go in as root but only after logging in as a user belonging to the admin group.

Last restart the SSH service for the changes to take effect.

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sudo /etc/init.d/ssh restart

Prevent SSH Brute Force Dictionary Attacks

As soon as it is on the Internet people will try to brute force attack your server over ssh. Basically they keep on pounding your system trying different passwords. fail2ban makes this kind of attack not worthwhile. After a chosen number of failed login attempts from the same ip address, fail2ban blocks that ip address for a set period of time. As constantly changing ip addresses is not a trivial task, the attacker will move on to another system.

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sudo apt-get install fail2ban

The fail2ban installer also starts fail2ban as a service right after installation completes.

Warning

This article is not yet fully transfered over from Google Sites.