os-hardening (Ansible Role)

Description

This role provides numerous security-related configurations, providing all-round base protection. It is intended to be compliant with the DevSec Linux Baseline.

It configures:

• Configures package management e.g. allows only signed packages
• Remove packages with known issues
• Configures pam and pam_limits module
• Shadow password suite configuration
• Configures system path permissions
• Disable core dumps via soft limits
• Restrict root Logins to System Console
• Set SUIDs
• Configures kernel parameters via sysctl
• Install and configure auditd

It will not:

• Update system packages
• Install security patches

Requirements

• Ansible 2.5.0

Warning

If you're using inspec to test your machines after applying this role, please make sure to add the connecting user to the os_ignore_users-variable. Otherwise inspec will fail. For more information, see issue #124.

If you're using Docker / Kubernetes+Docker you'll need to override the ipv4 ip forward sysctl setting.

- hosts: localhost
  roles:
    - dev-sec.os-hardening
  vars:
    sysctl_overwrite:
      # Enable IPv4 traffic forwarding.
      net.ipv4.ip_forward: 1

Variables

Name	Default Value	Description
os_desktop_enable	false	true if this is a desktop system, ie Xorg, KDE/GNOME/Unity/etc
os_env_extra_user_paths	[]	add additional paths to the user's PATH variable (default is empty).
os_env_umask	027	set default permissions for new files to 750
os_auth_pw_max_age	60	maximum password age (set to 99999 to effectively disable it)
os_auth_pw_min_age	7	minimum password age (before allowing any other password change)
os_auth_retries	5	the maximum number of authentication attempts, before the account is locked for some time
os_auth_lockout_time	600	time in seconds that needs to pass, if the account was locked due to too many failed authentication attempts
os_auth_timeout	60	authentication timeout in seconds, so login will exit if this time passes
os_auth_allow_homeless	false	true if to allow users without home to login
os_auth_pam_passwdqc_enable	true	true if you want to use strong password checking in PAM using passwdqc
os_auth_pam_passwdqc_options	"min=disabled,disabled,16,12,8"	set to any option line (as a string) that you want to pass to passwdqc
os_security_users_allow	[]	list of things, that a user is allowed to do. May contain change_user.
os_security_kernel_enable_module_loading	true	true if you want to allowed to change kernel modules once the system is running (eg modprobe, rmmod)
os_security_kernel_enable_core_dump	false	kernel is crashing or otherwise misbehaving and a kernel core dump is created
os_security_suid_sgid_enforce	true	true if you want to reduce SUID/SGID bits. There is already a list of items which are searched for configured, but you can also add your own
os_security_suid_sgid_blacklist	[]	a list of paths which should have their SUID/SGID bits removed
os_security_suid_sgid_whitelist	[]	a list of paths which should not have their SUID/SGID bits altered
os_security_suid_sgid_remove_from_unknown	false	true if you want to remove SUID/SGID bits from any file, that is not explicitly configured in a blacklist. This will make every Ansible-run search through the mounted filesystems looking for SUID/SGID bits that are not configured in the default and user blacklist. If it finds an SUID/SGID bit, it will be removed, unless this file is in your whitelist.
os_security_packages_clean	true	removes packages with known issues. See section packages.
os_selinux_state	enforcing	Set the SELinux state, can be either disabled, permissive, or enforcing.
os_selinux_policy	targeted	Set the SELinux polixy.
ufw_manage_defaults	true	true means apply all settings with ufw_ prefix
ufw_ipt_sysctl	''	by default it disables IPT_SYSCTL in /etc/default/ufw. If you want to overwrite /etc/sysctl.conf values using ufw - set it to your sysctl dictionary, for example /etc/ufw/sysctl.conf
ufw_default_input_policy	DROP	set default input policy of ufw to DROP
ufw_default_output_policy	ACCEPT	set default output policy of ufw to ACCEPT
ufw_default_forward_policy	DROP	set default forward policy of ufw to DROP
os_auditd_enabled	true	Set to false to disable installing and configuring auditd.
os_auditd_max_log_file_action	keep_logs	Defines the behaviour of auditd when its log file is filled up. Possible other values are described in the auditd.conf man page. The most common alternative to the default may be rotate.

Packages

We remove the following packages:

• xinetd (NSA, Chapter 3.2.1)
• inetd (NSA, Chapter 3.2.1)
• tftp-server (NSA, Chapter 3.2.5)
• ypserv (NSA, Chapter 3.2.4)
• telnet-server (NSA, Chapter 3.2.2)
• rsh-server (NSA, Chapter 3.2.3)
• prelink (open-scap)

Disabled filesystems

We disable the following filesystems, because they're most likely not used:

• "cramfs"
• "freevxfs"
• "jffs2"
• "hfs"
• "hfsplus"
• "squashfs"
• "udf"
• "vfat" # only if uefi is not in use

To prevent some of the filesystems from being disabled, add them to the os_filesystem_whitelist variable.

Installation

Install the role with ansible-galaxy:

ansible-galaxy install dev-sec.os-hardening

Example Playbook

- hosts: localhost
  roles:
    - dev-sec.os-hardening

Changing sysctl variables

If you want to override sysctl-variables, you can use the sysctl_overwrite variable (in older versions you had to override the whole sysctl_dict). So for example if you want to change the IPv4 traffic forwarding variable to 1, do it like this:

- hosts: localhost
  roles:
    - dev-sec.os-hardening
  vars:
    sysctl_overwrite:
      # Enable IPv4 traffic forwarding.
      net.ipv4.ip_forward: 1

Alternatively you can change Ansible's hash-behaviour to merge, then you only have to overwrite the single hash you need to. But please be aware that changing the hash-behaviour changes it for all your playbooks and is not recommended by Ansible.

Improving Kernel Audit logging

By default, any process that starts before the auditd daemon will have an AUID of 4294967295. To improve this and provide more accurate logging, it's recommended to add the kernel boot parameter audit=1 to you configuration. Without doing this, you will find that your auditd logs fail to properly audit all processes.

For more information, please see this upstream documentation and your system's boot loader documentation for how to configure additional kernel parameters.

Local Testing

The preferred way of locally testing the role is to use Docker. You will have to install Docker on your system. See Get started for a Docker package suitable to for your system.

You can also use vagrant and Virtualbox or VMWare to run tests locally. You will have to install Virtualbox and Vagrant on your system. See Vagrant Downloads for a vagrant package suitable for your system. For all our tests we use test-kitchen. If you are not familiar with test-kitchen please have a look at their guide.

Next install test-kitchen:

# Install dependencies
gem install bundler
bundle install

Testing with Docker

# fast test on one machine
bundle exec kitchen test default-ubuntu-1404

# test on all machines
bundle exec kitchen test

# for development
bundle exec kitchen create default-ubuntu-1404
bundle exec kitchen converge default-ubuntu-1404

Testing with Virtualbox

# fast test on one machine
KITCHEN_YAML=".kitchen.vagrant.yml" bundle exec kitchen test default-ubuntu-1404

# test on all machines
KITCHEN_YAML=".kitchen.vagrant.yml" bundle exec kitchen test

# for development
KITCHEN_YAML=".kitchen.vagrant.yml" bundle exec kitchen create default-ubuntu-1404
KITCHEN_YAML=".kitchen.vagrant.yml" bundle exec kitchen converge default-ubuntu-1404

For more information see test-kitchen

Contributors + Kudos

...

This role is mostly based on guides by:

• Arch Linux wiki, Sysctl hardening
• NSA: Guide to the Secure Configuration of Red Hat Enterprise Linux 5
• Ubuntu Security/Features
• Deutsche Telekom, Group IT Security, Security Requirements (German)

Thanks to all of you!

Contributing

See contributor guideline.

License and Author

• Author:: Sebastian Gumprich

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.