Guide to the Secure Configuration of Ubuntu 20.04
Rules, Groups, and Values defined within the XCCDF Benchmark
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Disable PubkeyAuthentication Authentication
Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms. To disable PubkeyAuthentication authentication, add or correct the following line in <code>/etc/ssh/sshd_...Rule Medium Severity -
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 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.d/00-compliancea...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 <code>/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf</code>: <pre>PermitRootLogin prohibit-passwor...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.d/00-compli...Rule Medium Severity -
Enable GSSAPI Authentication
Sites setup to use Kerberos or other GSSAPI Authenticaion require setting sshd to accept this authentication. To enable GSSAPI authentication, add or correct the following line in <code>/etc/ssh/...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 -
Force frequent session key renegotiation
The <code>RekeyLimit</code> parameter specifies how often the session key of the is renegotiated, both in terms of amount of data that may be transmitted and the time elapsed.<br> To decrease the d...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 -
Prevent remote hosts from connecting to the proxy display
The SSH daemon should prevent remote hosts from connecting to the proxy display. <br> The default SSH configuration for <code>X11UseLocalhost</code> is <code>yes</code>, which prevents remote hosts...Rule Medium Severity -
Action for auditd to take when disk errors
'The setting for disk_error_action in /etc/audit/auditd.conf, if multiple values are allowed write them separated by pipes as in "syslog|single|halt", for remediations the first value will be taken'Value -
Verify Permissions on Backup group File
To properly set the permissions of/etc/group-, run the command:$ sudo chmod 0644 /etc/group-
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 /var/log Directory
To properly set the owner of/var/log, run the command:$ sudo chown root /var/log
Rule Medium Severity -
Kernel panic on oops
To set the runtime status of the <code>kernel.panic_on_oops</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w kernel.panic_on_oops=1</pre> To make sure that the setting is p...Rule Medium Severity -
Verify permissions on Message of the Day Banner
To properly set the permissions of/etc/motd, run the command:$ sudo chmod 0644 /etc/motd
Rule Medium Severity -
Package "prelink" Must not be Installed
Theprelinkpackage can be removed with the following command:$ apt-get remove prelink
Rule Medium Severity -
Configure Periodic Execution of AIDE
At a minimum, AIDE should be configured to run a weekly scan. To implement a daily execution of AIDE at 4:05am using cron, add the following line to <code>/etc/crontab</code>: <pre>05 4 * * * root ...Rule Medium Severity -
Endpoint Protection Software
Endpoint protection security software that is not provided or supported by Canonical can be installed to provide complementary or duplicative security capabilities to those provided by the base p...Group -
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 -
Encrypt Partitions
Ubuntu 20.04 natively supports partition encryption through the Linux Unified Key Setup-on-disk-format (LUKS) technology. The easiest way to encrypt a partition is during installation time. <br> ...Rule High Severity -
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 -
Remove the GDM Package Group
By removing the <code>gdm3</code> package, the system no longer has GNOME installed installed. If X Windows is not installed then the system cannot boot into graphical user mode. This prevents th...Rule Medium Severity -
Disable Ctrl-Alt-Del Reboot Key Sequence in GNOME3
By default, <code>GNOME</code> will reboot the system if the <code>Ctrl-Alt-Del</code> key sequence is pressed. <br> <br> To configure the system to ignore the <code>Ctrl-Alt-Del</code> ke...Rule High Severity -
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 -
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 -
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 -
Warning Banners for System Accesses
Each system should expose as little information about itself as possible. <br> <br> System banners, which are typically displayed just before a login prompt, give out information about the s...Group -
Modify the System Login Banner
To configure the system login banner edit <code>/etc/issue</code>. Replace the default text with a message compliant with the local site policy or a legal disclaimer. The DoD required text is ei...Rule Medium Severity -
Modify the System Message of the Day Banner
To configure the system message banner edit <code>/etc/motd</code>. Replace the default text with a message compliant with the local site policy or a legal disclaimer. The DoD required text is eit...Rule Medium Severity -
Enable GNOME3 Login Warning Banner
In the default graphical environment, displaying a login warning banner in the GNOME Display Manager's login screen can be enabled on the login screen by setting <code>banner-message-enable</code> ...Rule Medium Severity -
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 Lockouts for Failed Password Attempts
The <code>pam_faillock</code> PAM module provides the capability to lock out user accounts after a number of failed login attempts. Its documentation is available in <code>/usr/share/doc/pam-VERSIO...Group -
Limit Password Reuse
Do not allow users to reuse recent passwords. This can be accomplished by using the <code>remember</code> option for the <code>pam_pwhistory</code> PAM modules. <br> <br> In the file <code...Rule Medium Severity -
Set Lockout Time for Failed Password Attempts
This rule configures the system to lock out accounts during a specified time period after a number of incorrect login attempts using <code>pam_faillock.so</code>. Ensure that the file <code>/etc/s...Rule Medium Severity -
Set Deny For Failed Password Attempts
The Ubuntu 20.04 operating system must lock an account after - at most - <xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_var_password...Rule Medium Severity -
Set Password Quality Requirements with pam_pwquality
The <code>pam_pwquality</code> PAM module can be configured to meet requirements for a variety of policies. <br> <br> For example, to configure <code>pam_pwquality</code> to require at lea...Group -
Ensure PAM Enforces Password Requirements - Minimum Digit Characters
The pam_pwquality module's <code>dcredit</code> parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many ...Rule Medium Severity -
Ensure PAM Enforces Password Requirements - Minimum Different Characters
The pam_pwquality module's <code>difok</code> parameter sets the number of characters in a password that must not be present in and old password during a password change. <br> <br> Modify...Rule Medium Severity -
Ensure PAM Enforces Password Requirements - Minimum Length
The pam_pwquality module's <code>minlen</code> parameter controls requirements for minimum characters required in a password. Add <code>minlen=<xccdf-1.2:sub idref="xccdf_org.ssgproject.content_val...Rule Medium Severity -
Ensure PAM Enforces Password Requirements - Minimum Special Characters
The pam_pwquality module's <code>ocredit=</code> parameter controls requirements for usage of special (or "other") characters in a password. When set to a negative number, any password will be requ...Rule Medium Severity -
Disable Ctrl-Alt-Del Reboot Activation
By default, <code>SystemD</code> will reboot the system if the <code>Ctrl-Alt-Del</code> key sequence is pressed. <br> <br> To configure the system to ignore the <code>Ctrl-Alt-Del</code> k...Rule High Severity -
Configure Smart Card Certificate Status Checking
Configure the operating system to do certificate status checking for PKI authentication. Modify all of the <code>cert_policy</code> lines in <code>/etc/pam_pkcs11/pam_pkcs11.conf</code> to include ...Rule Medium Severity -
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 Account Expiration Following Inactivity
To specify the number of days after a password expires (which signifies inactivity) until an account is permanently disabled, add or correct the following line in <code>/etc/default/useradd</code>:...Rule Medium Severity -
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 -
Set Password Warning Age
To specify how many days prior to password expiration that a warning will be issued to users, edit the file <code>/etc/login.defs</code> and add or correct the following line: <pre>PASS_WARN_AGE <...Rule Medium Severity -
Disable Accepting Packets Routed Between Local Interfaces
To set the runtime status of the <code>net.ipv4.conf.all.accept_local</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.all.accept_local=0</pre> To make sure t...Rule Medium Severity
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