Guide to the Secure Configuration of Ubuntu 16.04
Rules, Groups, and Values defined within the XCCDF Benchmark
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Disable SSH Support for .rhosts Files
SSH can emulate the behavior of the obsolete rsh command in allowing users to enable insecure access to their accounts via <code>.rhosts</code> files. <br> The default SSH configuration disables su...Rule Medium Severity -
Disable SSH Support for Rhosts RSA Authentication
SSH can allow authentication through the obsolete rsh command through the use of the authenticating user's SSH keys. This should be disabled. <br> <br> To ensure this behavior is disabled, ...Rule Medium Severity -
Disable SSH Root Login
The root user should never be allowed to login to a system directly over a network. To disable root login via SSH, add or correct the following line in <code>/etc/ssh/sshd_config</code>: <pre>Pe...Rule Medium Severity -
Disable SSH root Login with a Password (Insecure)
To disable password-based root logins over SSH, add or correct the following line in/etc/ssh/sshd_config:PermitRootLogin prohibit-password
Rule Medium Severity -
Disable SSH TCP Forwarding
The <code>AllowTcpForwarding</code> parameter specifies whether TCP forwarding is permitted. To disable TCP forwarding, add or correct the following line in <code>/etc/ssh/sshd_config</code>: <p...Rule Medium Severity -
Disable SSH Support for User Known Hosts
SSH can allow system users to connect to systems if a cache of the remote systems public keys is available. This should be disabled. <br> <br> To ensure this behavior is disabled, add or c...Rule Medium Severity -
Do Not Allow SSH Environment Options
Ensure that users are not able to override environment variables of the SSH daemon. <br> The default SSH configuration disables environment processing. The appropriate configuration is used if no v...Rule Medium Severity -
Enable PAM
UsePAM Enables the Pluggable Authentication Module interface. If set to “yes” this will enable PAM authentication using ChallengeResponseAuthentication and PasswordAuthentication in addition to PAM...Rule Medium Severity -
Enable Public Key Authentication
Enable SSH login with public keys. <br> The default SSH configuration enables authentication based on public keys. The appropriate configuration is used if no value is set for <code>PubkeyAuthentic...Rule Medium Severity -
Enable Use of Strict Mode Checking
SSHs <code>StrictModes</code> option checks file and ownership permissions in the user's home directory <code>.ssh</code> folder before accepting login. If world- writable permissions are found, lo...Rule Medium Severity -
Enable SSH Warning Banner
To enable the warning banner and ensure it is consistent across the system, add or correct the following line in <code>/etc/ssh/sshd_config</code>: <pre>Banner /etc/issue</pre> Another section c...Rule Medium Severity -
Enable SSH Warning Banner
To enable the warning banner and ensure it is consistent across the system, add or correct the following line in <code>/etc/ssh/sshd_config</code>: <pre>Banner /etc/issue.net</pre> Another sectio...Rule Medium Severity -
Enable Encrypted X11 Forwarding
By default, remote X11 connections are not encrypted when initiated by users. SSH has the capability to encrypt remote X11 connections when SSH's <code>X11Forwarding</code> option is enabled. <br> ...Rule High Severity -
Limit Users' SSH Access
By default, the SSH configuration allows any user with an account to access the system. There are several options available to limit which users and group can access the system via SSH. It is recom...Rule Unknown Severity -
Ensure SSH LoginGraceTime is configured
The <code>LoginGraceTime</code> parameter to the SSH server specifies the time allowed for successful authentication to the SSH server. The longer the Grace period is the more open unauthenticated ...Rule Medium Severity -
Set LogLevel to INFO
The INFO parameter specifices that record login and logout activity will be logged. <br> The default SSH configuration sets the log level to INFO. The appropriate configuration is used if no value ...Rule Low Severity -
Set SSH Daemon LogLevel to VERBOSE
The <code>VERBOSE</code> parameter configures the SSH daemon to record login and logout activity. To specify the log level in SSH, add or correct the following line in <code>/etc/ssh/sshd_config<...Rule Medium Severity -
Set SSH authentication attempt limit
The <code>MaxAuthTries</code> parameter specifies the maximum number of authentication attempts permitted per connection. Once the number of failures reaches half this value, additional failures ar...Rule Medium Severity -
Set SSH MaxSessions limit
The <code>MaxSessions</code> parameter specifies the maximum number of open sessions permitted from a given connection. To set MaxSessions edit <code>/etc/ssh/sshd_config</code> as follows: <pre>Ma...Rule Medium Severity -
Ensure SSH MaxStartups is configured
The MaxStartups parameter specifies the maximum number of concurrent unauthenticated connections to the SSH daemon. Additional connections will be dropped until authentication succeeds or the Login...Rule Medium Severity -
Enable Use of Privilege Separation
When enabled, SSH will create an unprivileged child process that has the privilege of the authenticated user. To enable privilege separation in SSH, add or correct the following line in the <code>/...Rule Medium Severity -
Ensure /dev/shm is configured
The <code>/dev/shm</code> is a traditional shared memory concept. One program will create a memory portion, which other processes (if permitted) can access. If <code>/dev/shm</code> is not configur...Rule Low Severity -
Ensure PAM Displays Last Logon/Access Notification
To configure the system to notify users of last logon/access using <code>pam_lastlog</code>, add or correct the <code>pam_lastlog</code> settings in <code>/etc/pam.d/login</code> to include <code>s...Rule Low Severity -
Prevent Login to Accounts With Empty Password
If an account is configured for password authentication but does not have an assigned password, it may be possible to log into the account without authentication. Remove any instances of the <code>...Rule High Severity -
Restrict unprivileged access to the kernel syslog
Enforce restrictions on unprivileged users reading the kernel syslog via dmesg(8). The configuration that was used to build kernel is available at <code>/boot/config-*</code>. To check the con...Rule Medium Severity -
Verify Permissions on group File
To properly set the permissions of/etc/group, run the command:$ sudo chmod 0644 /etc/group
Rule Medium Severity -
Verify User Who Owns Backup group File
To properly set the owner of/etc/group-, run the command:$ sudo chown root /etc/group-
Rule Medium Severity -
Verify Permissions on shadow File
To properly set the permissions of/etc/shadow, run the command:$ sudo chmod 0640 /etc/shadow
Rule Medium Severity -
Verify that System Executable Have Root Ownership
<pre>/bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbin</pre> All these directories should be owned by the <code>root</code> user. If any directory <i>DIR</i> in these directories is foun...Rule Medium Severity -
The Chrony package is installed
System time should be synchronized between all systems in an environment. This is typically done by establishing an authoritative time server or set of servers and having all systems synchronize th...Rule Medium Severity -
Disk Partitioning
To ensure separation and protection of data, there are top-level system directories which should be placed on their own physical partition or logical volume. The installer's default partitioning sc...Group -
GNOME Desktop Environment
GNOME is a graphical desktop environment bundled with many Linux distributions that allow users to easily interact with the operating system graphically rather than textually. The GNOME Graphical D...Group -
Configure GNOME Login Screen
In the default GNOME desktop, the login is displayed after system boot and can display user accounts, allow users to reboot the system, and allow users to login automatically and/or with a guest ac...Group -
Sudo
<code>Sudo</code>, which stands for "su 'do'", provides the ability to delegate authority to certain users, groups of users, or system administrators. When configured for system users and/or groups...Group -
Ensure Users Re-Authenticate for Privilege Escalation - sudo !authenticate
The sudo <code>!authenticate</code> option, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the <code>!authe...Rule Medium Severity -
Ensure Users Re-Authenticate for Privilege Escalation - sudo
The sudo <code>NOPASSWD</code> and <code>!authenticate</code> option, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making ...Rule Medium Severity -
Explicit arguments in sudo specifications
All commands in the sudoers file must strictly specify the arguments allowed to be used for a given user. If the command is supposed to be executed only without arguments, pass "" as an argument in...Rule Medium Severity -
Ensure gnutls-utils is installed
Thegnutls-utilspackage can be installed with the following command:$ apt-get install gnutls-utils
Rule Medium Severity -
Updating Software
The <code>apt_get</code> command line tool is used to install and update software packages. The system also provides a graphical software update tool in the <b>System</b> menu, in the <b>Administra...Group -
Protect Accounts by Configuring PAM
PAM, or Pluggable Authentication Modules, is a system which implements modular authentication for Linux programs. PAM provides a flexible and configurable architecture for authentication, and it sh...Group -
Set Account Expiration Parameters
Accounts can be configured to be automatically disabled after a certain time period, meaning that they will require administrator interaction to become usable again. Expiration of accounts after in...Group -
Set Password Expiration Parameters
The file <code>/etc/login.defs</code> controls several password-related settings. Programs such as <code>passwd</code>, <code>su</code>, and <code>login</code> consult <code>/etc/login.defs</code> ...Group -
Set Password Maximum Age
To specify password maximum age for new accounts, edit the file <code>/etc/login.defs</code> and add or correct the following line: <pre>PASS_MAX_DAYS <xccdf-1.2:sub idref="xccdf_org.ssgproject.con...Rule Medium Severity -
Ensure There Are No Accounts With Blank or Null Passwords
Check the "/etc/shadow" file for blank passwords with the following command: <pre>$ sudo awk -F: '!$2 {print $1}' /etc/shadow</pre> If the command returns any results, this is a finding. Configure ...Rule High Severity -
Restrict Virtual Console Root Logins
To restrict root logins through the (deprecated) virtual console devices, ensure lines of this form do not appear in/etc/securetty:vc/1 vc/2 vc/3 vc/4
Rule Medium Severity -
Ensure the Logon Failure Delay is Set Correctly in login.defs
To ensure the logon failure delay controlled by <code>/etc/login.defs</code> is set properly, add or correct the <code>FAIL_DELAY</code> setting in <code>/etc/login.defs</code> to read as follows: ...Rule Medium Severity -
Enable Kernel Parameter to Enforce DAC on Hardlinks
To set the runtime status of the <code>fs.protected_hardlinks</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w fs.protected_hardlinks=1</pre> To make sure that the setting ...Rule Medium Severity -
Configure Low Address Space To Protect From User Allocation
This is the portion of low virtual memory which should be protected from userspace allocation. This configuration is available from kernel 3.14, but may be available if backported by distros. The ...Rule Medium Severity -
Limit the Number of Concurrent Login Sessions Allowed Per User
Limiting the number of allowed users and sessions per user can limit risks related to Denial of Service attacks. This addresses concurrent sessions for a single account and does not address concurr...Rule Low Severity -
Ensure the Default Umask is Set Correctly in login.defs
To ensure the default umask controlled by <code>/etc/login.defs</code> is set properly, add or correct the <code>UMASK</code> setting in <code>/etc/login.defs</code> to read as follows: <pre>UMASK ...Rule Medium Severity
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