Guide to the Secure Configuration of Ubuntu 1604

with profile Profile for ANSSI DAT-NT28 Minimal Level
This profile contains items to be applied systematically.
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 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 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 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 TitleProfile for ANSSI DAT-NT28 Minimal Level
Profile IDxccdf_org.ssgproject.content_profile_anssi_np_nt28_minimal

Revision History

Current version: 0.1.31

  • draft (as of 2017-03-31)

Platforms

  • cpe:/o:canonical:ubuntu_linux:16.04

Table of Contents

  1. System Settings
    1. File Permissions and Masks
  2. Services
    1. Deprecated services
    2. APT service configuration

Checklist

contains 9 rules

System Settings   [ref]group

Contains rules that check correct system settings.

contains 4 rules

File Permissions and Masks   [ref]group

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.

contains 4 rules

Verify Permissions on Important Files and Directories   [ref]group

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.

contains 4 rules
contains 4 rules

Verify Permissions and ownership on shadow File   [ref]rule

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

Remediation Shell script:   (show)

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

Verify Permissions and ownership on gshadow File   [ref]rule

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

Remediation Shell script:   (show)

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

Verify Permissions and ownership on passwd File   [ref]rule

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

Remediation Shell script:   (show)

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

Verify Permissions and ownership on group File   [ref]rule

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

Remediation Shell script:   (show)

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

Services   [ref]group

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.

contains 5 rules

Deprecated services   [ref]group

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.

contains 4 rules

Uninstall the telnet server   [ref]rule

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

Remediation Shell script:   (show)

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

Uninstall the inet-based telnet server   [ref]rule

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

Remediation Shell script:   (show)

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

Uninstall the ssl compliant telnet server   [ref]rule

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

Identifiers:  CCE-

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

Remediation Shell script:   (show)

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

Uninstall the nis package   [ref]rule

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

Identifiers:  CCE-

Remediation Shell script:   (show)

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

APT service configuration   [ref]group

The apt service manage the package management and update of the whole system. Its configuration need to be properly defined to ensure efficient security updates, packages and repository authentication and proper lifecycle management.

contains 1 rule

Disable unauthenticated repositories in APT configuration   [ref]rule

Unauthenticated repositories should not be used for updates.

Rationale:

Repositories hosts all packages that will be intsalled on the system during update. If a repository is not authenticated, the associated packages can't be trusted, and then should not be installed localy.

Severity:  low

References:  NT28(R15)

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