Guide to the Secure Configuration of Ubuntu 1604

with profile Standard System Security Profile for Ubuntu 16
This profile contains rules to ensure standard security baseline of an Ubuntu 16 system. Regardless of your system's workload all of these checks should pass.
This guide presents a catalog of security-relevant configuration settings for Ubuntu 1604. It is a rendering of content structured in the eXtensible Configuration Checklist Description Format (XCCDF) in order to support security automation. The SCAP content is is available in the config_item="scap-security-guide" package which is developed at https://www.open-scap.org/security-policies/scap-security-guide.

Providing system administrators with such guidance informs them how to securely configure systems under their control in a variety of network roles. Policy makers and baseline creators can use this catalog of settings, with its associated references to higher-level security control catalogs, in order to assist them in security baseline creation. This guide is a italics="catalog, not a checklist," and satisfaction of every item is not likely to be possible or sensible in many operational scenarios. However, the XCCDF format enables granular selection and adjustment of settings, and their association with OVAL and OCIL content provides an automated checking capability. Transformations of this document, and its associated automated checking content, are capable of providing baselines that meet a diverse set of policy objectives. Some example XCCDF italics="Profiles", which are selections of items that form checklists and can be used as baselines, are available with this guide. They can be processed, in an automated fashion, with tools that support the Security Content Automation Protocol (SCAP). The DISA STIG for Ubuntu 1604, which provides required settings for US Department of Defense systems, is one example of a baseline created from this guidance.
Do not attempt to implement any of the settings in this guide without first testing them in a non-operational environment. The creators of this guidance assume no responsibility whatsoever for its use by other parties, and makes no guarantees, expressed or implied, about its quality, reliability, or any other characteristic.

Profile Information

Profile TitleStandard System Security Profile for Ubuntu 16
Profile IDxccdf_org.ssgproject.content_profile_standard

CPE Platforms

  • cpe:/o:canonical:ubuntu_linux:16.04

Revision History

Current version: 0.1.39

  • draft (as of 2021-02-28)

Table of Contents

  1. Services
    1. Deprecated services
    2. Generic required services
    3. SSH Server
  2. System Settings
    1. Configure Syslog
    2. Hardening the filesystem
    3. File Permissions and Masks

Checklist

Group   Guide to the Secure Configuration of Ubuntu 1604   Group contains 19 groups and 36 rules
Group   Services   Group contains 4 groups and 16 rules

[ref]   The best protection against vulnerable software is running less software. This section describes how to review the software which Ubuntu 1604 installs on a system and disable software which is not needed. It then enumerates the software packages installed on a default Ubuntu 1604 system and provides guidance about which ones can be safely disabled.

Ubuntu 1604 provides a convenient minimal install option that essentially installs the bare necessities for a functional system. When building Ubuntu 1604 systems, it is highly recommended to select the minimal packages and then build up the system from there.

Group   Deprecated services   Group contains 5 rules

[ref]   Some deprecated software services impact the overall system security due to their behavior (leak of confidentiality in network exchange, usage as uncontrolled communication channel, risk associated with the service due to its old age, etc.

Rule   Uninstall the nis package   [ref]

The support for Yellowpages should not be installed unless it is required.

Rationale:

NIS is the historical SUN service for central account management, more and more replaced by LDAP. NIS does not support efficiently security constraints, ACL, etc. and should not be used.

Severity: 
low
Rule ID:xccdf_org.ssgproject.content_rule_package_nis_removed
Identifiers and References

Identifiers:  CCE-



Complexity:low
Disruption:low
Strategy:disable
# CAUTION: This remediation script will remove nis
#	   from the system, and may remove any packages
#	   that depend on nis. Execute this
#	   remediation AFTER testing on a non-production
#	   system!

apt-get remove --purge nis


Complexity:low
Disruption:low
Strategy:disable
- name: Ensure nis is removed
  package:
    name="{{item}}"
    state=absent
  with_items:
    - nis
  tags:
    - package_nis_removed
    - low_severity
    - disable_strategy
    - low_complexity
    - low_disruption
    - CCE-


Complexity:low
Disruption:low
Strategy:disable
include remove_nis

class remove_nis {
  package { 'nis':
    ensure => 'purged',
  }
}

Rule   Uninstall the inet-based telnet server   [ref]

The inet-based telnet daemon should be uninstalled.

Rationale:

telnet allows clear text communications, and does not protect any data transmission between client and server. Any confidential data can be listened and no integrity checking is made.

Severity: 
high
Rule ID:xccdf_org.ssgproject.content_rule_package_inetutils-telnetd_removed
Identifiers and References

Identifiers:  CCE-

References:  NT007(R03), AC-17(8), CM-7



Complexity:low
Disruption:low
Strategy:disable
# CAUTION: This remediation script will remove inetutils-telnetd
#	   from the system, and may remove any packages
#	   that depend on inetutils-telnetd. Execute this
#	   remediation AFTER testing on a non-production
#	   system!

apt-get remove --purge inetutils-telnetd


Complexity:low
Disruption:low
Strategy:disable
- name: Ensure inetutils-telnetd is removed
  package:
    name="{{item}}"
    state=absent
  with_items:
    - inetutils-telnetd
  tags:
    - package_inetutils-telnetd_removed
    - high_severity
    - disable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-AC-17(8)
    - NIST-800-53-CM-7


Complexity:low
Disruption:low
Strategy:disable
include remove_inetutils-telnetd

class remove_inetutils-telnetd {
  package { 'inetutils-telnetd':
    ensure => 'purged',
  }
}

Rule   Uninstall the ntpdate package   [ref]

ntpdate is a historical ntp synchronization client for unixes. It sould be uninstalled.

Rationale:

ntpdate is an old not security-compliant ntp client. It should be replaced by modern ntp clients such as ntpd, able to use cryptographic mechanisms integrated in NTP.

Severity: 
low
Rule ID:xccdf_org.ssgproject.content_rule_package_ntpdate_removed
Identifiers and References

Identifiers:  CCE-



Complexity:low
Disruption:low
Strategy:disable
# CAUTION: This remediation script will remove ntpdate
#	   from the system, and may remove any packages
#	   that depend on ntpdate. Execute this
#	   remediation AFTER testing on a non-production
#	   system!

apt-get remove --purge ntpdate


Complexity:low
Disruption:low
Strategy:disable
- name: Ensure ntpdate is removed
  package:
    name="{{item}}"
    state=absent
  with_items:
    - ntpdate
  tags:
    - package_ntpdate_removed
    - low_severity
    - disable_strategy
    - low_complexity
    - low_disruption
    - CCE-


Complexity:low
Disruption:low
Strategy:disable
include remove_ntpdate

class remove_ntpdate {
  package { 'ntpdate':
    ensure => 'purged',
  }
}

Rule   Uninstall the ssl compliant telnet server   [ref]

The telnet daemon, even with ssl support, should be uninstalled.

Rationale:

telnet, even with ssl support, should not be installed. When remote shell is required, up-to-date ssh daemon can be used.

Severity: 
high
Rule ID:xccdf_org.ssgproject.content_rule_package_telnetd-ssl_removed
Identifiers and References

Identifiers:  CCE-

References:  NT007(R02), AC-17(8), CM-7



Complexity:low
Disruption:low
Strategy:disable
# CAUTION: This remediation script will remove telnetd-ssl
#	   from the system, and may remove any packages
#	   that depend on telnetd-ssl. Execute this
#	   remediation AFTER testing on a non-production
#	   system!

apt-get remove --purge telnetd-ssl


Complexity:low
Disruption:low
Strategy:disable
- name: Ensure telnetd-ssl is removed
  package:
    name="{{item}}"
    state=absent
  with_items:
    - telnetd-ssl
  tags:
    - package_telnetd-ssl_removed
    - high_severity
    - disable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-AC-17(8)
    - NIST-800-53-CM-7


Complexity:low
Disruption:low
Strategy:disable
include remove_telnetd-ssl

class remove_telnetd-ssl {
  package { 'telnetd-ssl':
    ensure => 'purged',
  }
}

Rule   Uninstall the telnet server   [ref]

The telnet daemon should be uninstalled.

Rationale:

telnet allows clear text communications, and does not protect any data transmission between client and server. Any confidential data can be listened and no integrity checking is made.

Severity: 
high
Rule ID:xccdf_org.ssgproject.content_rule_package_telnetd_removed
Identifiers and References

Identifiers:  CCE-

References:  NT007(R03), AC-17(8), CM-7



Complexity:low
Disruption:low
Strategy:disable
# CAUTION: This remediation script will remove telnetd
#	   from the system, and may remove any packages
#	   that depend on telnetd. Execute this
#	   remediation AFTER testing on a non-production
#	   system!

apt-get remove --purge telnetd


Complexity:low
Disruption:low
Strategy:disable
- name: Ensure telnetd is removed
  package:
    name="{{item}}"
    state=absent
  with_items:
    - telnetd
  tags:
    - package_telnetd_removed
    - high_severity
    - disable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-AC-17(8)
    - NIST-800-53-CM-7


Complexity:low
Disruption:low
Strategy:disable
include remove_telnetd

class remove_telnetd {
  package { 'telnetd':
    ensure => 'purged',
  }
}
Group   Generic required services   Group contains 6 rules

[ref]   Some services need to be deployed in order to ensure basic verifications and reporting on GNU/Linux operating systems. Each of these service take part in the administrability of the system.

Rule   Install the cron service   [ref]

The Cron service should be installed.

Rationale:

The cron service allow periodic job execution, needed for almost all administrative tasks and services (software update, log rotating, etc.). Access to cron service should be restricted to administrative accounts only.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_package_cron_installed
Identifiers and References

Identifiers:  CCE-

References:  NT28(R50), CM-7



Complexity:low
Disruption:low
Strategy:enable
- name: Ensure cron is installed
  package:
    name="{{item}}"
    state=present
  with_items:
    - cron
  tags:
    - package_cron_installed
    - medium_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-CM-7


Complexity:low
Disruption:low
Strategy:enable
include install_cron

class install_cron {
  package { 'cron':
    ensure => 'installed',
  }
}

Rule   Install the ntp service   [ref]

The ntpd service should be installed.

Rationale:

Time synchronization (using NTP) is required by almost all network and administrative tasks (syslog, cryptographic based services (authentication, etc.), etc.). Ntpd is regulary maintained and updated, supporting security features such as RFC 5906.

Severity: 
high
Rule ID:xccdf_org.ssgproject.content_rule_package_ntp_installed
Identifiers and References

Identifiers:  CCE-

References:  NT012(R03), CCI-000160, AU-8(1), Req-10.4



Complexity:low
Disruption:low
Strategy:enable
- name: Ensure ntp is installed
  package:
    name="{{item}}"
    state=present
  with_items:
    - ntp
  tags:
    - package_ntp_installed
    - high_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-AU-8(1)
    - PCI-DSS-Req-10.4


Complexity:low
Disruption:low
Strategy:enable
include install_ntp

class install_ntp {
  package { 'ntp':
    ensure => 'installed',
  }
}

Rule   Enable the cron service   [ref]

The Cron service should be enabled.

Rationale:

The cron service allow periodic job execution, needed for almost all administrative tasks and services (software update, log rotating, etc.). Access to cron service should be restricted to administrative accounts only.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_service_cron_enabled
Identifiers and References

Identifiers:  CCE-

References:  CM-7



Complexity:low
Disruption:low
Strategy:enable
- name: Enable service cron
  service:
    name="{{item}}"
    enabled="yes"
    state="started"
  with_items:
    - cron
  tags:
    - service_cron_enabled
    - medium_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-CM-7

Rule   install the auditd service   [ref]

The auditd service should be installed.

Rationale:

The auditd service is an access monitoring and accounting daemon, watching system calls to audit any access, in comparision with potential local access control policy such as SELinux policy.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_package_auditd_installed
Identifiers and References

Identifiers:  CCE-

References:  NT28(R50)



Complexity:low
Disruption:low
Strategy:enable
- name: Ensure auditd is installed
  package:
    name="{{item}}"
    state=present
  with_items:
    - auditd
  tags:
    - package_auditd_installed
    - medium_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - CCE-


Complexity:low
Disruption:low
Strategy:enable
include install_auditd

class install_auditd {
  package { 'auditd':
    ensure => 'installed',
  }
}

Rule   Enable the ntpd service   [ref]

The ntpd service should be enabled.

Rationale:

Time synchronization (using NTP) is required by almost all network and administrative tasks (syslog, cryptographic based services (authentication, etc.), etc.). Ntpd is regulary maintained and updated, supporting security features such as RFC 5906.

Severity: 
high
Rule ID:xccdf_org.ssgproject.content_rule_service_ntpd_enabled
Identifiers and References

Identifiers:  CCE-

References:  NT012(R03), CCI-000160, AU-8(1), Req-10.4



Complexity:low
Disruption:low
Strategy:enable
- name: Enable service ntpd
  service:
    name="{{item}}"
    enabled="yes"
    state="started"
  with_items:
    - ntpd
  tags:
    - service_ntpd_enabled
    - high_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-AU-8(1)
    - PCI-DSS-Req-10.4

Rule   Enable the auditd service   [ref]

The auditd service should be enabled.

Rationale:

The auditd service is an access monitoring and accounting daemon, watching system calls to audit any access, in comparision with potential local access control policy such as SELinux policy.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_service_auditd_enabled
Identifiers and References

Identifiers:  CCE-

References:  NT28(R50), CCI-000347, CCI-000157, CCI-000172, CCI-000880, CCI-001353, CCI-001462, CCI-001487, CCI-001115, CCI-001454, CCI-000067, CCI-000158, CCI-000831, CCI-001190, CCI-001312, CCI-001263, CCI-000130, CCI-000120, CCI-001589, AC-17(1), AU-1(b), AU-10, AU-12(a), AU-12(c), IR-5, Req-10



Complexity:low
Disruption:low
Strategy:enable
- name: Enable service auditd
  service:
    name="{{item}}"
    enabled="yes"
    state="started"
  with_items:
    - auditd
  tags:
    - service_auditd_enabled
    - medium_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - CCE-
    - NIST-800-53-AC-17(1)
    - NIST-800-53-AU-1(b)
    - NIST-800-53-AU-10
    - NIST-800-53-AU-12(a)
    - NIST-800-53-AU-12(c)
    - NIST-800-53-IR-5
    - PCI-DSS-Req-10
Group   SSH Server   Group contains 1 group and 5 rules

[ref]   The SSH protocol is recommended for remote access (remote login and secure remote file transfer). SSH provides both confidentiality and integrity for exchanged data but needs to be configured properly in term of:
Cryptography usage, according to the current CVEs associated to the various cryptographic modes
Authentication and autorization, depending on your needs but requiring some specific initial generic security
consideration in the OpenSSH configuration writing More detailed information is available from the OpenSSH project's website http://www.openssh.org. The Ubuntu package for server side implementation is called openssh-server.

Group   Configure OpenSSH Server if deployed   Group contains 5 rules

[ref]   If the system needs to act as an SSH server, then certain changes should be made to the OpenSSH daemon configuration file /etc/ssh/sshd_config. The following recommendations can be applied to this file. See the sshd_config(5) man page for more detailed information.

Rule   Allow Only SSH Protocol 2   [ref]

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

Protocol 2

Rationale:

SSH protocol version 1 suffers from design flaws that result in security vulnerabilities and should not be used.

Severity: 
high
Rule ID:xccdf_org.ssgproject.content_rule_sshd_allow_only_protocol2
Identifiers and References

Identifiers:  CCE-

References:  NT007(R1), AC-17(7), IA-5(1)(c)

Rule   Disable SSH Access via Empty Passwords   [ref]

To explicitly disallow remote login from accounts with empty passwords, add or correct the following line in /etc/ssh/sshd_config:

PermitEmptyPasswords no
Any accounts with empty passwords should be disabled immediately, and PAM configuration should prevent users from being able to assign themselves empty passwords.

Rationale:

Configuring this setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere.

Severity: 
high
Rule ID:xccdf_org.ssgproject.content_rule_sshd_disable_empty_passwords
Identifiers and References

Identifiers:  CCE-

References:  NT007(R17), AC-3

Rule   Set SSH Idle Timeout Interval   [ref]

SSH allows administrators to set an idle timeout interval. After this interval has passed, the idle user will be automatically logged out.

To set an idle timeout interval, edit the following line in /etc/ssh/sshd_config as follows:

ClientAliveInterval interval
The timeout interval is given in seconds. To have a timeout of 15 minutes, set interval to 900.

If a shorter timeout has already been set for the login shell, that value will preempt any SSH setting made here. Keep in mind that some processes may stop SSH from correctly detecting that the user is idle.

Rationale:

Causing idle users to be automatically logged out guards against compromises one system leading trivially to compromises on another.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_sshd_set_idle_timeout
Identifiers and References

Identifiers:  CCE-

References:  AC-2(5), SA-8, Req-8.1.8

Rule   Set SSH Client Alive Count   [ref]

To ensure the SSH idle timeout occurs precisely when the ClientAliveCountMax is set, edit /etc/ssh/sshd_config as follows:

ClientAliveCountMax 0

Rationale:

This ensures a user login will be terminated as soon as the ClientAliveCountMax is reached.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_sshd_set_keepalive
Identifiers and References

Identifiers:  CCE-

References:  AC-2(5), SA-8

Group   System Settings   Group contains 13 groups and 20 rules

[ref]   Contains rules that check correct system settings.

Group   Configure Syslog   Group contains 2 groups and 6 rules

[ref]   The syslog service has been the default Unix logging mechanism for many years. It has a number of downsides, including inconsistent log format, lack of authentication for received messages, and lack of authentication, encryption, or reliable transport for messages sent over a network. However, due to its long history, syslog is a de facto standard which is supported by almost all Unix applications.

In Ubuntu 1604, rsyslog has replaced syslog as the syslog daemon of choice, and it includes some additional security features such as reliable, connection-oriented (i.e. TCP) transmission of logs, the option to log to database formats, and the encryption of log data en route to a central logging server. This section discusses how to configure rsyslog for best effect, and how to use tools provided with the system to maintain and monitor logs. Yet, it is also possible to install syslog-ng to manage local and server-side logging services. Both are tested here, to let the administrator choose.

Group   Ensure Proper Configuration of Log Files   Group contains 3 rules

[ref]   The file /etc/rsyslog.conf controls where log message are written. These are controlled by lines called rules, which consist of a selector and an action. These rules are often customized depending on the role of the system, the requirements of the environment, and whatever may enable the administrator to most effectively make use of log data. The default rules in Ubuntu 1604 are:

auth,authpriv.*			/var/log/auth.log
*.*;auth,authpriv.none          -/var/log/syslog
daemon.*                        -/var/log/daemon.log
kern.*                          -/var/log/kern.log
lpr.*                           -/var/log/lpr.log
mail.*                          -/var/log/mail.log
user.*                          -/var/log/user.log
mail.info                       -/var/log/mail.info
mail.warn                       -/var/log/mail.warn
mail.err                        /var/log/mail.err
news.crit                       /var/log/news/news.crit
news.err                        /var/log/news/news.err
news.notice                     -/var/log/news/news.notice
See the man page rsyslog.conf(5) for more information. Note that the rsyslog daemon is configured to use traditional timestamping to be understood by any log processing program. For high precision timestamping, comment the following line in /etc/rsyslog.conf:
$ ActionFileDefaultTemplate RSYSLOG_TraditionalFileFormat

Rule   Ensure Log Files Are Owned By Appropriate Group   [ref]

The group-owner of all log files written by rsyslog should be root. These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's group owner:

$ ls -l LOGFILE
If the owner is not adm, run the following command to correct this:
$ sudo chgrp adm LOGFILE

Rationale:

The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_rsyslog_files_groupownership
Identifiers and References

References:  NT28(R46), NT28(R5), CCI-001314, AC-6, SI-11, Req-10.5.1, Req-10.5.2

Rule   Ensure Log Files Are Owned By Appropriate User   [ref]

The owner of all log files written by rsyslog should be root. These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's owner:

$ ls -l LOGFILE
If the owner is not root, run the following command to correct this:
$ sudo chown root LOGFILE

Rationale:

The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_rsyslog_files_ownership
Identifiers and References

References:  NT28(R46), NT28(R5), CCI-001314, AC-6, SI-11, Req-10.5.1, Req-10.5.2

Rule   Ensure System Log Files Have Correct Permissions   [ref]

The file permissions for all log files written by rsyslog should be set to 640, or more restrictive. These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's permissions:

$ ls -l LOGFILE
If the permissions are not 640 or more restrictive, run the following command to correct this:
$ sudo chmod 0640 LOGFILE

Rationale:

Log files can contain valuable information regarding system configuration. If the system log files are not protected unauthorized users could change the logged data, eliminating their forensic value.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_rsyslog_files_permissions
Identifiers and References

References:  NT28(R36), 5.1.4, CCI-001314, SI-11, Req-10.5.1, Req-10.5.2

Group   Ensure All Logs are Rotated by <tt>logrotate</tt>   Group contains 1 rule

[ref]   Edit the file /etc/logrotate.d/rsyslog. Find the first line, which should look like this (wrapped for clarity):

/var/log/messages /var/log/secure /var/log/maillog /var/log/spooler \
  /var/log/boot.log /var/log/cron {
Edit this line so that it contains a one-space-separated listing of each log file referenced in /etc/rsyslog.conf.

All logs in use on a system must be rotated regularly, or the log files will consume disk space over time, eventually interfering with system operation. The file /etc/logrotate.d/syslog is the configuration file used by the logrotate program to maintain all log files written by syslog. By default, it rotates logs weekly and stores four archival copies of each log. These settings can be modified by editing /etc/logrotate.conf, but the defaults are sufficient for purposes of this guide.

Note that logrotate is run nightly by the cron job /etc/cron.daily/logrotate. If particularly active logs need to be rotated more often than once a day, some other mechanism must be used.

Rule   Ensure Logrotate Runs Periodically   [ref]

The logrotate utility allows for the automatic rotation of log files. The frequency of rotation is specified in /etc/logrotate.conf, which triggers a cron task. To configure logrotate to run daily, add or correct the following line in /etc/logrotate.conf:

# rotate log files frequency
daily

Rationale:

Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_ensure_logrotate_activated
Identifiers and References

References:  CCI-000366, AU-9, Req-10.7

Rule   Enable rsyslog Service   [ref]

The rsyslog service provides syslog-style logging by default on Ubuntu 1604. The rsyslog service can be enabled with the following command:

$ sudo chkconfig --level 2345 rsyslog on

Rationale:

The rsyslog service must be running in order to provide logging services, which are essential to system administration.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_service_rsyslog_enabled
Identifiers and References

References:  NT28(R46), NT28(R5), 5.1.2, CCI-001311, CCI-001312, CCI-001557, CCI-001851, AU-4(1), AU-12



Complexity:low
Disruption:low
Strategy:enable
- name: Enable service rsyslog
  service:
    name="{{item}}"
    enabled="yes"
    state="started"
  with_items:
    - rsyslog
  tags:
    - service_rsyslog_enabled
    - medium_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - NIST-800-53-AU-4(1)
    - NIST-800-53-AU-12

Rule   Ensure rsyslog is Installed   [ref]

Rsyslog is installed by default. The rsyslog package can be installed with the following command:

# apt-get install rsyslog

Rationale:

The rsyslog package provides the rsyslog daemon, which provides system logging services.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_package_rsyslog_installed
Identifiers and References

References:  NT28(R46), NT28(R5), 5.1.1, CCI-001311, CCI-001312, AU-9(2)



Complexity:low
Disruption:low
Strategy:enable
- name: Ensure rsyslog is installed
  package:
    name="{{item}}"
    state=present
  with_items:
    - rsyslog
  tags:
    - package_rsyslog_installed
    - medium_severity
    - enable_strategy
    - low_complexity
    - low_disruption
    - NIST-800-53-AU-9(2)


Complexity:low
Disruption:low
Strategy:enable
include install_rsyslog

class install_rsyslog {
  package { 'rsyslog':
    ensure => 'installed',
  }
}
Group   Hardening the filesystem   Group contains 2 groups and 7 rules

[ref]   Hardening the filesystem and its usage is an efficient way to ensure an efficient separation of services, data and configurations while ensuring a more precise management of filesystem level access rights, enabling deactivation of some specific rights at the filesystem level. Moreover, the Linux Virtual file system support various hardening mechanisms that can be set using sysctl.

Group   Partitioning   Group contains 5 rules

[ref]   Separating various locations of the file systems in different partitions allows a more restrictive segregation, distinctly from one location to another. Moreover, some native restrictions can be made by partitioning, such as no hard link between different filesystems, and reduce the corruption impact to the affected filesystem instead of the entire system. The last gain is to allow a differenciated usage of storage media, depending on the operational needs (speed, resilience, etc.).

Rule   Ensure /home Located On Separate Partition   [ref]

If user home directories will be stored locally, create a separate partition for /home at installation time (or migrate it later using LVM). If /home will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later.

Rationale:

Ensuring that /home is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_partition_for_home
Identifiers and References

References:  NT28(R12), CCI-001208, SC-32

Rule   Ensure /var Located On Separate Partition   [ref]

The /var directory is used by daemons and other system services to store frequently-changing data. Ensure that /var has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

Ensuring that /var is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the /var directory to contain world-writable directories installed by other software packages.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_partition_for_var
Identifiers and References

References:  NT28(R12), SC-32

Rule   Ensure /tmp Located On Separate Partition   [ref]

The /tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM (when non-ephemeral is needed) or use tmpfs if possible.

Rationale:

The /tmp partition is used as temporary storage by many programs. Placing /tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_partition_for_tmp
Identifiers and References

References:  NT28(R12), SC-32

Rule   Ensure /var/log/audit Located On Separate Partition   [ref]

Audit logs are stored in the /var/log/audit directory. Ensure that it has its own partition or logical volume at installation time, or migrate it later using LVM. Make absolutely certain that it is large enough to store all audit logs that will be created by the auditing daemon.

Rationale:

Placing /var/log/audit in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_partition_for_var_log_audit
Identifiers and References

References:  AU-4, AU-9, SC-32

Rule   Ensure /var/log Located On Separate Partition   [ref]

System logs are stored in the /var/log directory. Ensure that it has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

Placing /var/log in its own partition enables better separation between log files and other files in /var/.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_partition_for_var_log
Identifiers and References

References:  NT28(R12), NT28(R47), AU-9, SC-32

Group   filesystem rights management   Group contains 2 rules

[ref]   Adding filesystem specific hardening seriously limits various exploitation vectors based on filesystem invalid usage, such as invalid file types in invalid places (devices or setuid root files in external media, executable file in insecure filesystems, etc.). Some of these hardening require an efficient system partitioning.

Group   File Permissions and Masks   Group contains 6 groups and 7 rules

[ref]   Traditional Unix security relies heavily on file and directory permissions to prevent unauthorized users from reading or modifying files to which they should not have access.

Several of the commands in this section search filesystems for files or directories with certain characteristics, and are intended to be run on every local partition on a given system. When the variable PART appears in one of the commands below, it means that the command is intended to be run repeatedly, with the name of each local partition substituted for PART in turn.

The following command prints a list of all xfs partitions on the local system, which is the default filesystem for Red Hat Enterprise Linux 7 installations:

$ mount -t xfs | awk '{print $3}'
For any systems that use a different local filesystem type, modify this command as appropriate.

Group   Verify Permissions on Important Files and Directories   Group contains 2 groups and 5 rules

[ref]   Permissions for many files on a system must be set restrictively to ensure sensitive information is properly protected. This section discusses important permission restrictions which can be verified to ensure that no harmful discrepancies have arisen.

Group   Verify Permissions on Files with Local Account Information and Credentials   Group contains 4 rules

Rule   Verify Permissions and ownership on group File   [ref]

To properly set the permissions of /etc/passwd, run the command:

$ sudo chmod 0644 /etc/passwd
To properly set the owner of /etc/passwd, run the command:
$ sudo chown root /etc/passwd 
To properly set the group owner of /etc/passwd, run the command:
$ sudo chgrp root /etc/passwd 

Rationale:

The /etc/shadow file contains information about the groups that are configured on the system. Protection of this file is critical for system security.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_file_permissions_etc_group
Identifiers and References

References:  AC-6



Complexity:low
Disruption:low
Strategy:configure
chmod 0644 /etc/group


Complexity:low
Disruption:low
Strategy:configure
- name: Ensure permission 0644 on /etc/group
  file:
    path="{{item}}"
    mode=0644
  with_items:
    - /etc/group
  tags:
    - file_permissions_etc_group
    - medium_severity
    - configure_strategy
    - low_complexity
    - low_disruption
    - NIST-800-53-AC-6

Rule   Verify Permissions and ownership on shadow File   [ref]

To properly set the permissions of /etc/shadow, run the command:

$ sudo chmod 0640 /etc/shadow
To properly set the owner of /etc/shadow, run the command:
$ sudo chown root /etc/shadow 
To properly set the group owner of /etc/shadow, run the command:
$ sudo chgrp shadow /etc/shadow 

Rationale:

The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_file_permissions_etc_shadow
Identifiers and References

References:  NT28(R36), AC-6, Req-8.7.c



Complexity:low
Disruption:low
Strategy:configure
chmod 0640 /etc/shadow


Complexity:low
Disruption:low
Strategy:configure
- name: Ensure permission 0640 on /etc/shadow
  file:
    path="{{item}}"
    mode=0640
  with_items:
    - /etc/shadow
  tags:
    - file_permissions_etc_shadow
    - medium_severity
    - configure_strategy
    - low_complexity
    - low_disruption
    - NIST-800-53-AC-6
    - PCI-DSS-Req-8.7.c

Rule   Verify Permissions and ownership on gshadow File   [ref]

To properly set the permissions of /etc/gshadow, run the command:

$ sudo chmod 0640 /etc/gshadow
To properly set the owner of /etc/gshadow, run the command:
$ sudo chown root /etc/gshadow 
To properly set the group owner of /etc/gshadow, run the command:
$ sudo chgrp shadow /etc/gshadow 

Rationale:

The /etc/shadow file contains group password hashes. Protection of this file is critical for system security.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_file_permissions_etc_gshadow
Identifiers and References

References:  NT28(R36), AC-6



Complexity:low
Disruption:low
Strategy:configure
chmod 0640 /etc/gshadow


Complexity:low
Disruption:low
Strategy:configure
- name: Ensure permission 0640 on /etc/gshadow
  file:
    path="{{item}}"
    mode=0640
  with_items:
    - /etc/gshadow
  tags:
    - file_permissions_etc_gshadow
    - medium_severity
    - configure_strategy
    - low_complexity
    - low_disruption
    - NIST-800-53-AC-6

Rule   Verify Permissions and ownership on passwd File   [ref]

To properly set the permissions of /etc/passwd, run the command:

$ sudo chmod 0644 /etc/passwd
To properly set the owner of /etc/passwd, run the command:
$ sudo chown root /etc/passwd 
To properly set the group owner of /etc/passwd, run the command:
$ sudo chgrp root /etc/passwd 

Rationale:

The /etc/shadow file contains information about the users that are configured on the system. Protection of this file is critical for system security.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_file_permissions_etc_passwd
Identifiers and References

References:  AC-6



Complexity:low
Disruption:low
Strategy:configure
chmod 0644 /etc/passwd


Complexity:low
Disruption:low
Strategy:configure
- name: Ensure permission 0644 on /etc/passwd
  file:
    path="{{item}}"
    mode=0644
  with_items:
    - /etc/passwd
  tags:
    - file_permissions_etc_passwd
    - medium_severity
    - configure_strategy
    - low_complexity
    - low_disruption
    - NIST-800-53-AC-6
Group   Verify permissions on files containing sensitive informations about the system   Group contains 1 rule

[ref]   Various files contains sensitive informations that can leads to specific weaknesses or give structural informations for local exploits.

Rule   Verify that local System.map file (if exists) is readable only by root   [ref]

Files containing sensitive informations should be protected by restrictive permissions. Most of the time, there is no need that these files need to be read by any non-root user To properly set the permissions of /boot/System.map-*, run the command:

$ sudo chmod 0600 /boot/System.map-*
To properly set the owner of /boot/System.map-*, run the command:
$ sudo chown root /boot/System.map-* 

Rationale:

The System.map file contains information about kernel symbols and can give some hints to generate local exploitation.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_file_permissions_boot_system_map
Identifiers and References

References:  NT28(R13)



Complexity:low
Disruption:low
Strategy:configure
find /boot -regex '^/boot/System\.map.*$' -exec chmod 0600 {} \;
Group   Restrict Programs from Dangerous Execution Patterns   Group contains 2 groups and 2 rules

[ref]   The recommendations in this section are designed to ensure that the system's features to protect against potentially dangerous program execution are activated. These protections are applied at the system initialization or kernel level, and defend against certain types of badly-configured or compromised programs.

Group   Disable Core Dumps   Group contains 1 rule

[ref]   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 access these files. The core dump files may also contain sensitive information, or unnecessarily occupy large amounts of disk space.

Once a hard limit is set in /etc/security/limits.conf, a user cannot increase that limit within his or her own session. If access to core dumps is required, consider restricting them to only certain users or groups. See the limits.conf man page for more information.

The core dumps of setuid programs are further protected. The sysctl variable fs.suid_dumpable controls whether the kernel allows core dumps from these programs at all. The default value of 0 is recommended.

Rule   Disable Core Dumps for SUID programs   [ref]

To set the runtime status of the fs.suid_dumpable kernel parameter, run the following command:

$ sudo sysctl -w fs.suid_dumpable=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
fs.suid_dumpable = 0

Rationale:

The core dump of a setuid program is more likely to contain wve data, as the program itself runs with greater privileges than the user who initiated execution of the program. Disabling the ability for any setuid program to write a core file decreases the risk of unauthorized access of such data.

Severity: 
unknown
Rule ID:xccdf_org.ssgproject.content_rule_sysctl_fs_suid_dumpable
Identifiers and References

References:  NT28(R23), 1.6.1, SI-11



Complexity:low
Disruption:medium
Reboot:true
Strategy:disable
- name: Ensure sysctl fs.suid_dumpable is set to 0
  sysctl:
    name: fs.suid_dumpable
    value: 0
    state: present
    reload: yes
  tags:
    - sysctl_fs_suid_dumpable
    - unknown_severity
    - disable_strategy
    - low_complexity
    - medium_disruption
    - NIST-800-53-SI-11
Group   Enable ExecShield   Group contains 1 rule

[ref]   ExecShield describes kernel features that provide protection against exploitation of memory corruption errors such as buffer overflows. These features include random placement of the stack and other memory regions, prevention of execution in memory that should only hold data, and special handling of text buffers. These protections are enabled by default on 32-bit systems and controlled through sysctl variables kernel.exec-shield and kernel.randomize_va_space. On the latest 64-bit systems, kernel.exec-shield cannot be enabled or disabled with sysctl.

Rule   Enable Randomized Layout of Virtual Address Space   [ref]

To set the runtime status of the kernel.randomize_va_space kernel parameter, run the following command:

$ sudo sysctl -w kernel.randomize_va_space=2
If this is not the system's default value, add the following line to /etc/sysctl.conf:
kernel.randomize_va_space = 2

Rationale:

Address space layout randomization (ASLR) makes it more difficult for an attacker to predict the location of attack code they have introduced into a process's address space during an attempt at exploitation. Additionally, ASLR makes it more difficult for an attacker to know the location of existing code in order to re-purpose it using return oriented programming (ROP) techniques.

Severity: 
medium
Rule ID:xccdf_org.ssgproject.content_rule_sysctl_kernel_randomize_va_space
Identifiers and References

References:  NT28(R23), 1.6.1, SC-30(2)



Complexity:low
Disruption:medium
Reboot:true
Strategy:disable
- name: Ensure sysctl kernel.randomize_va_space is set to 2
  sysctl:
    name: kernel.randomize_va_space
    value: 2
    state: present
    reload: yes
  tags:
    - sysctl_kernel_randomize_va_space
    - medium_severity
    - disable_strategy
    - low_complexity
    - medium_disruption
    - NIST-800-53-SC-30(2)
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