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Guide to the Secure Configuration of Ubuntu 20.04

Rules, Groups, and Values defined within the XCCDF Benchmark

  • Verify Permissions on System.map Files

    The System.map files are symbol map files generated during the compilation of the Linux kernel. They contain the mapping between kernel symbols and their corresponding memory addresses. In general,...
    Rule Low Severity
    Show

  • Ensure All Files Are Owned by a Group

    If any file is not group-owned by a group present in /etc/group, the cause of the lack of group-ownership must be investigated. Following this, those files should be deleted or assigned to an appro...
    Rule Medium Severity
    Show

  • Ensure All Files Are Owned by a User

    If any files are not owned by a user, then the cause of their lack of ownership should be investigated. Following this, the files should be deleted or assigned to an appropriate user. Locate the m...
    Rule Medium Severity
    Show

  • 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
    Show

  • Verify User Who Owns shadow File

    To properly set the owner of /etc/shadow, run the command: 
    $ sudo chown root /etc/shadow
    Rule Medium Severity
    Show

  • Enable Kernel Parameter to Enforce DAC on Symlinks

    To set the runtime status of the <code>fs.protected_symlinks</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w fs.protected_symlinks=1</pre> To make sure that the setting is...
    Rule Medium Severity
    Show

  • Verify Group Who Owns Backup group File

    To properly set the group owner of /etc/group-, run the command: 
    $ sudo chgrp root /etc/group-
    Rule Medium Severity
    Show

  • Verify Group Who Owns Backup gshadow File

    To properly set the group owner of /etc/gshadow-, run the command: 
    $ sudo chgrp shadow /etc/gshadow-
    Rule Medium Severity
    Show

  • Verify Group Who Owns Backup passwd File

    To properly set the group owner of /etc/passwd-, run the command: 
    $ sudo chgrp root /etc/passwd-
    Rule Medium Severity
    Show

  • Verify User Who Owns Backup shadow File

    To properly set the group owner of /etc/shadow-, run the command: 
    $ sudo chgrp shadow /etc/shadow-
    Rule Medium Severity
    Show

  • Verify Group Who Owns group File

    To properly set the group owner of /etc/group, run the command: 
    $ sudo chgrp root /etc/group
    Rule Medium Severity
    Show

  • Verify Group Who Owns gshadow File

    To properly set the group owner of /etc/gshadow, run the command: 
    $ sudo chgrp shadow /etc/gshadow
    Rule Medium Severity
    Show

  • Verify Group Who Owns passwd File

    To properly set the group owner of /etc/passwd, run the command: 
    $ sudo chgrp root /etc/passwd
    Rule Medium Severity
    Show

  • Verify Group Who Owns shadow File

    To properly set the group owner of /etc/shadow, run the command: 
    $ sudo chgrp shadow /etc/shadow
    Rule Medium Severity
    Show

  • 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
    Show

  • Verify User Who Owns Backup gshadow File

    To properly set the owner of /etc/gshadow-, run the command: 
    $ sudo chown root /etc/gshadow-
    Rule Medium Severity
    Show

  • Verify User Who Owns Backup passwd File

    To properly set the owner of /etc/passwd-, run the command: 
    $ sudo chown root /etc/passwd-
    Rule Medium Severity
    Show

  • Verify Group Who Owns Backup shadow File

    To properly set the owner of /etc/shadow-, run the command: 
    $ sudo chown root /etc/shadow-
    Rule Medium Severity
    Show

  • Verify User Who Owns group File

    To properly set the owner of /etc/group, run the command: 
    $ sudo chown root /etc/group
    Rule Medium Severity
    Show

  • Verify that Shared Library Directories Have Root Group Ownership

    System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: <pre>/lib /lib64 /usr/lib /usr/lib64 </pr...
    Rule Medium Severity
    Show

  • Verify that System Executable Directories Have Restrictive Permissions

    System executables are stored in the following directories by default: <pre>/bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbin</pre> These directories should not be group-writable or worl...
    Rule Medium Severity
    Show

  • Verify that Shared Library Directories Have Restrictive Permissions

    System-wide shared library directories, which contain are linked to executables during process load time or run time, are stored in the following directories by default: <pre>/lib /lib64 /usr/lib /...
    Rule Medium Severity
    Show

  • Verify that Shared Library Files Have Root Ownership

    System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default: <pre>/lib /lib64 /usr/lib /usr/lib64 </pr...
    Rule Medium Severity
    Show

  • Verify the system-wide library files in directories "/lib", "/lib64", "/usr/lib/" and "/usr/lib64" are group-owned by root.

    System-wide library files are stored in the following directories by default: <pre>/lib /lib64 /usr/lib /usr/lib64 </pre> All system-wide shared library files should be protected from unauthorised ...
    Rule Medium Severity
    Show

  • Disable Mounting of freevxfs

    To configure the system to prevent the <code>freevxfs</code> kernel module from being loaded, add the following line to the file <code>/etc/modprobe.d/freevxfs.conf</code>: <pre>install freevxfs /...
    Rule Low Severity
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  • Disable Mounting of udf

    To configure the system to prevent the <code>udf</code> kernel module from being loaded, add the following line to the file <code>/etc/modprobe.d/udf.conf</code>: <pre>install udf /bin/false</pre>...
    Rule Low Severity
    Show

  • 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_restrict=1</pre> To make sure that the setting is...
    Rule Low Severity
    Show

  • Disable Core Dumps

    A core dump file is the memory image of an executable program when it was terminated by the operating system due to errant behavior. In most cases, only software developers legitimately need to acc...
    Group
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  • Restrict Exposed Kernel Pointer Addresses Access

    To set the runtime status of the <code>kernel.kptr_restrict</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w kernel.kptr_restrict=<xccdf-1.2:sub idref="xccdf_org.ssgproject...
    Rule Medium Severity
    Show

  • Enable Randomized Layout of Virtual Address Space

    To set the runtime status of the <code>kernel.randomize_va_space</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w kernel.randomize_va_space=2</pre> To make sure that the se...
    Rule Medium Severity
    Show

  • SELinux

    SELinux is a feature of the Linux kernel which can be used to guard against misconfigured or compromised programs. SELinux enforces the idea that programs should be limited in what files they can a...
    Group
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  • Services

    The best protection against vulnerable software is running less software. This section describes how to review the software which Ubuntu 20.04 installs on a system and disable software which is not...
    Group
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  • Disable Avahi Publishing

    To prevent Avahi from publishing its records, edit <code>/etc/avahi/avahi-daemon.conf</code> and ensure the following line appears in the <code>[publish]</code> section: <pre>disable-publishing=yes...
    Rule Low Severity
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  • Disable Avahi Server Software

    The avahi-daemon service can be disabled with the following command: 
    $ sudo systemctl mask --now avahi-daemon.service
    Rule Medium Severity
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  • Verify Group Who Owns cron.hourly

    To properly set the group owner of /etc/cron.hourly, run the command: 
    $ sudo chgrp root /etc/cron.hourly
    Rule Medium Severity
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  • Verify Permissions on cron.monthly

    To properly set the permissions of /etc/cron.monthly, run the command: 
    $ sudo chmod 0700 /etc/cron.monthly
    Rule Medium Severity
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  • Restrict at and cron to Authorized Users if Necessary

    The <code>/etc/cron.allow</code> and <code>/etc/at.allow</code> files contain lists of users who are allowed to use <code>cron</code> and at to delay execution of processes. If these files exist an...
    Group
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  • DHCP

    The Dynamic Host Configuration Protocol (DHCP) allows systems to request and obtain an IP address and other configuration parameters from a server. <br> <br> This guide recommends configuring...
    Group
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  • Minimize the DHCP-Configured Options

    Create the file <code>/etc/dhcp/dhclient.conf</code>, and add an appropriate setting for each of the ten configuration settings which can be obtained via DHCP. For each setting, do one of the follo...
    Rule Unknown Severity
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  • Uninstall bind Package

    The named service is provided by the bind package. The bind package can be removed with the following command: 
    $ apt-get remove bind
    Rule Low Severity
    Show

  • FTP Server

    FTP is a common method for allowing remote access to files. Like telnet, the FTP protocol is unencrypted, which means that passwords and other data transmitted during the session can be captured an...
    Group
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  • Configure Firewalls to Protect the FTP Server

    By default, <code>iptables</code> blocks access to the ports used by the web server. To configure <code>iptables</code> to allow port 21 traffic, one must edit <code>/etc/sysconfig/iptables</code>...
    Rule Unknown Severity
    Show

  • Uninstall cyrus-imapd Package

    The cyrus-imapd package can be removed with the following command: 
    $ apt-get remove cyrus-imapd
    Rule Unknown Severity
    Show

  • Ensure LDAP client is not installed

    The Lightweight Directory Access Protocol (LDAP) is a service that provides a method for looking up information from a central database. The <code>lapd-utils</code> package can be removed with the ...
    Rule Low Severity
    Show

  • Mail Server Software

    Mail servers are used to send and receive email over the network. Mail is a very common service, and Mail Transfer Agents (MTAs) are obvious targets of network attack. Ensure that systems are not r...
    Group
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  • Configure System to Forward All Mail through a specific host

    Set up a relay host that will act as a gateway for all outbound email. Edit the file <code>/etc/postfix/main.cf</code> to ensure that only the following <code>relayhost</code> line appears: <pre>re...
    Rule Medium Severity
    Show

  • Uninstall nfs-kernel-server Package

    The nfs-kernel-server package can be removed with the following command: 
    $ apt-get remove nfs-kernel-server
    Rule Low Severity
    Show

  • Disable Network File Systems (netfs)

    The netfs script manages the boot-time mounting of several types of networked filesystems, of which NFS and Samba are the most common. If these filesystem types are not in use, the script can be di...
    Rule Unknown Severity
    Show

  • Uninstall rpcbind Package

    The rpcbind utility maps RPC services to the ports on which they listen. RPC processes notify rpcbind when they start, registering the ports they are listening on and the RPC program numbers they e...
    Rule Low Severity
    Show

  • 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
    Show

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