Guide to the Secure Configuration of Ubuntu 20.04
Rules, Groups, and Values defined within the XCCDF Benchmark
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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 an...Rule Unknown Severity -
Enable SSH Print Last Log
Ensure that SSH will display the date and time of the last successful account logon. <br> The default SSH configuration enables print of the date a...Rule Medium 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 ...Rule Medium 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 t...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 failur...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 <co...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 ...Rule Medium Severity -
Use Only FIPS 140-2 Validated Ciphers
Limit the ciphers to those algorithms which are FIPS-approved. Counter (CTR) mode is also preferred over cipher-block chaining (CBC) mode. The foll...Rule Medium Severity -
Use Only FIPS 140-2 Validated Ciphers
Limit the ciphers to those algorithms which are FIPS-approved. The following line in <code>/etc/ssh/sshd_config</code> demonstrates use of FIPS-app...Rule Medium Severity -
Use Only FIPS 140-2 Validated Key Exchange Algorithms
Limit the key exchange algorithms to those which are FIPS-approved. Add or modify the following line in <code>/etc/ssh/sshd_config</code> <pre>Kex...Rule Medium Severity -
Use Only FIPS 140-2 Validated MACs
Limit the MACs to those hash algorithms which are FIPS-approved. The following line in <code>/etc/ssh/sshd_config</code> demonstrates use of FIPS-a...Rule Medium Severity -
Use Only FIPS 140-2 Validated MACs
Limit the MACs to those hash algorithms which are FIPS-approved. The following line in <code>/etc/ssh/sshd_config</code> demonstrates use of FIPS-a...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...Rule Medium Severity -
Use Only Strong Key Exchange algorithms
Limit the Key Exchange to strong algorithms. The following line in <code>/etc/ssh/sshd_config</code> demonstrates use of those: <pre>KexAlgorithms ...Rule Medium Severity -
Strengthen Firewall Configuration if Possible
If the SSH server is expected to only receive connections from the local network, then strengthen the default firewall rule for the SSH service to ...Group -
System Security Services Daemon
The System Security Services Daemon (SSSD) is a system daemon that provides access to different identity and authentication providers such as Red H...Group -
SSSD certificate_verification option
Value of the certificate_verification option in the SSSD config.Value -
Configure SSSD to Expire Offline Credentials
SSSD should be configured to expire offline credentials after 1 day. To configure SSSD to expire offline credentials, set <code>offline_credential...Rule Medium Severity -
System Security Services Daemon (SSSD) - LDAP
The System Security Services Daemon (SSSD) is a system daemon that provides access to different identity and authentication providers such as Red H...Group -
SSSD LDAP Backend Client CA Certificate Location
Path of a directory that contains Certificate Authority certificates.Value -
USBGuard daemon
The USBGuard daemon enforces the USB device authorization policy for all USB devices.Group -
X Window System
The X Window System implementation included with the system is called X.org.Group -
Disable X Windows
Unless there is a mission-critical reason for the system to run a graphical user interface, ensure X is not set to start automatically at boot and ...Group -
Remove the X Windows Package Group
By removing the xorg-x11-server-common package, the system no longer has X Windows installed. If X Windows is not installed then the system cannot ...Rule Medium Severity -
Introduction
The purpose of this guidance is to provide security configuration recommendations and baselines for the Ubuntu 20.04 operating system. Recommended ...Group -
General Principles
The following general principles motivate much of the advice in this guide and should also influence any configuration decisions that are not expli...Group -
Encrypt Transmitted Data Whenever Possible
Data transmitted over a network, whether wired or wireless, is susceptible to passive monitoring. Whenever practical solutions for encrypting such ...Group -
Least Privilege
Grant the least privilege necessary for user accounts and software to perform tasks. For example, <code>sudo</code> can be implemented to limit aut...Group -
Minimize Software to Minimize Vulnerability
The simplest way to avoid vulnerabilities in software is to avoid installing that software. On Ubuntu 20.04,the Package Manager (originally <a href...Group -
Run Different Network Services on Separate Systems
Whenever possible, a server should be dedicated to serving exactly one network service. This limits the number of other services that can be compro...Group -
Configure Security Tools to Improve System Robustness
Several tools exist which can be effectively used to improve a system's resistance to and detection of unknown attacks. These tools can improve rob...Group -
How to Use This Guide
Readers should heed the following points when using the guide.Group -
Formatting Conventions
Commands intended for shell execution, as well as configuration file text, are featured in a <code>monospace font</code>. <i>Italics</i> are used t...Group -
Read Sections Completely and in Order
Each section may build on information and recommendations discussed in prior sections. Each section should be read and understood completely; instr...Group -
Reboot Required
A system reboot is implicitly required after some actions in order to complete the reconfiguration of the system. In many cases, the changes will n...Group -
Root Shell Environment Assumed
Most of the actions listed in this document are written with the assumption that they will be executed by the root user running the <code>/bin/bash...Group -
Test in Non-Production Environment
This guidance should always be tested in a non-production environment before deployment. This test environment should simulate the setup in which t...Group -
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 e...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 -
Restrict Access to Kernel Message Buffer
To set the runtime status of the <code>kernel.dmesg_restrict</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w kernel.dmesg...Rule Low Severity -
389 Directory Server
389 Directory Server is a popular open-source LDAP server for Linux.Group -
SSH Strong MACs by FIPS
Specify the FIPS approved MACs (Message Authentication Code) algorithms that are used for data integrity protection by the SSH server.Value -
Configure AIDE To Notify Personnel if Baseline Configurations Are Altered
The operating system file integrity tool must be configured to notify designated personnel of any changes to configurations.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) ca...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 i...Rule Low Severity -
Lock Accounts After Failed Password Attempts
This rule configures the system to lock out accounts after a number of incorrect login attempts using <code>pam_faillock.so</code>. pam_faillock.so...Rule Medium Severity -
Set Interval For Counting Failed Password Attempts
Utilizing <code>pam_faillock.so</code>, the <code>fail_interval</code> directive configures the system to lock out an account after a number of inc...Rule Medium Severity -
Do Not Show System Messages When Unsuccessful Logon Attempts Occur
This rule ensures the system prevents informative messages from being presented to the user pertaining to logon information after a number of incor...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_fail...Rule Medium Severity -
Enable Smart Card Logins in PAM
This requirement only applies to components where this is specific to the function of the device or has the concept of an organizational user (e.g....Rule Medium Severity
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