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Guide to the Secure Configuration of Ubuntu 20.04

Rules, Groups, and Values defined within the XCCDF Benchmark

  • Verify Ownership on SSH Server Public *.pub Key Files

    SSH server public keys, files that match the /etc/ssh/*.pub glob, must be owned by root user.
    Rule Medium Severity
    Show

  • Verify Permissions on SSH Server config file

    To properly set the permissions of /etc/ssh/sshd_config, run the command: 
    $ sudo chmod 0600 /etc/ssh/sshd_config
    Rule Medium Severity
    Show

  • Verify Permissions on SSH Server Private *_key Key Files

    SSH server private keys - files that match the <code>/etc/ssh/*_key</code> glob, have to have restricted permissions. If those files are owned by the <code>root</code> user and the <code>root</code...
    Rule Medium Severity
    Show

  • Verify Permissions on SSH Server Public *.pub Key Files

    To properly set the permissions of /etc/ssh/*.pub, run the command: 
    $ sudo chmod 0644 /etc/ssh/*.pub
    Rule Medium Severity
    Show

  • Configure OpenSSH Server if Necessary

    If the system needs to act as an SSH server, then certain changes should be made to the OpenSSH daemon configuration file <code>/etc/ssh/sshd_config</code>. The following recommendations can be app...
    Group
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  • SSH RekeyLimit - size

    Specify the size component of the rekey limit.
    Value
    Show

  • SSH RekeyLimit - size

    Specify the size component of the rekey limit.
    Value
    Show

  • SSH Compression Setting

    Specify the compression setting for SSH connections.
    Value
    Show

  • SSH Privilege Separation Setting

    Specify whether and how sshd separates privileges when handling incoming network connections.
    Value
    Show

  • SSH LoginGraceTime setting

    Configure parameters for how long the servers stays connected before the user has successfully logged in
    Value
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  • SSH MaxStartups setting

    Configure parameters for maximum concurrent unauthenticated connections to the SSH daemon.
    Value
    Show

  • Set SSH Client Alive Count Max

    The SSH server sends at most <code>ClientAliveCountMax</code> messages during a SSH session and waits for a response from the SSH client. The option <code>ClientAliveInterval</code> configures time...
    Rule Medium Severity
    Show

  • Allow Only SSH Protocol 2

    Only SSH protocol version 2 connections should be permitted. The default setting in <code>/etc/ssh/sshd_config</code> is correct, and can be verified by ensuring that the following line appears: <p...
    Rule High Severity
    Show

  • Disable Compression Or Set Compression to delayed

    Compression is useful for slow network connections over long distances but can cause performance issues on local LANs. If use of compression is required, it should be enabled only after a user has ...
    Rule Medium Severity
    Show

  • 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.d/00-complianceascode-hardening.conf</code>: <pre>Bann...
    Rule Medium Severity
    Show

  • 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
    Show

  • 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
    Show

  • 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
    Show

  • 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 and time of the last login. The appropriate configu...
    Rule Medium Severity
    Show

  • 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
    Show

  • 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
    Show

  • 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
    Show

  • 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
    Show

  • 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 following line in <code>/etc/ssh/sshd_config</code> de...
    Rule Medium Severity
    Show

  • 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>KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-ni...
    Rule Medium Severity
    Show

  • 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-approved MACs: <pre>MACs hmac-sha2-512,hmac-sha2-2...
    Rule Medium Severity
    Show

  • 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-approved MACs: <pre>MACs <xccdf-1.2:sub idref="xccd...
    Rule Medium Severity
    Show

  • 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
    Show

  • 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 <xccdf-1.2:sub idref="xccdf_org.ssgproject.content...
    Rule Medium Severity
    Show

  • 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 Hat's IdM, Microsoft's AD, openLDAP, MIT Kerberos, ...
    Group
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  • X Window System

    The X Window System implementation included with the system is called X.org.
    Group
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  • 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 remove the X Windows software packages. There is u...
    Group
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  • 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
    Show

  • 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
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  • 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
    Show

  • 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 module requires multiple entries in pam files. Th...
    Rule Medium Severity
    Show

  • 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 incorrect login attempts within a specified time peri...
    Rule Medium Severity
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  • 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 incorrect login attempts using <code>pam_faillock.so</c...
    Rule Medium Severity
    Show

  • 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., VPN, proxy capability). This does not apply to a...
    Rule Medium Severity
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  • 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
    Show

  • Ensure the Group Used by pam_wheel.so Module Exists on System and is Empty

    Ensure that the group <code><xccdf-1.2:sub idref="xccdf_org.ssgproject.content_value_var_pam_wheel_group_for_su" use="legacy"></xccdf-1.2:sub></code> referenced by <code>var_pam_wheel_group_for_su<...
    Rule Medium Severity
    Show

  • Enforce Usage of pam_wheel with Group Parameter for su Authentication

    To ensure that only users who are members of the group set in the <code>group</code> option of <code>pam_wheel.so</code> module can run commands with altered privileges through the <code>su</code> ...
    Rule Medium Severity
    Show

  • Set SSH Client Alive Count Max to zero

    The SSH server sends at most <code>ClientAliveCountMax</code> messages during a SSH session and waits for a response from the SSH client. The option <code>ClientAliveInterval</code> configures time...
    Rule Medium Severity
    Show

  • 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
    Show

  • Ensure nftables Default Deny Firewall Policy

    Base chain policy is the default verdict that will be applied to packets reaching the end of the chain. There are two policies: accept (Default) and drop. If the policy is set to accept, the firewa...
    Rule Medium Severity
    Show

  • Ensure auditd Collects Information on the Use of Privileged Commands - ssh-keysign

    At a minimum, the audit system should collect the execution of privileged commands for all users and root. If the <code>auditd</code> daemon is configured to use the <code>augenrules</code> program...
    Rule Medium Severity
    Show

  • Type of hostname to record the audit event

    Type of hostname to record the audit event
    Value
    Show

  • Disable SSH Access via Empty Passwords

    Disallow SSH login with empty passwords. The default SSH configuration disables logins with empty passwords. The appropriate configuration is used if no value is set for <code>PermitEmptyPasswords<...
    Rule High Severity
    Show

  • Disable GSSAPI Authentication

    Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like GSSAPI. <br> The default SSH configuration disallows authentications based on GSSAPI. The appropriate c...
    Rule Medium Severity
    Show

  • Disable Kerberos Authentication

    Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like Kerberos. <br> The default SSH configuration disallows authentication validation through Kerberos. The ...
    Rule Medium Severity
    Show

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