os-hardening (Ansible Role)

Description

This roles provides numerous security-related configurations, providing all-round base protection.

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

It will not:

• Update system packages
• Install security patches

Requirements

• Ansible

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
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_sysrq	false	sysrq is a 'magical' key combo you can hit which the kernel will respond to regardless of whatever else it is doing, unless it is completely locked up.
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.
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

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)

Example Playbook

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

Changing sysctl variables

If you want to overwrite sysctl-variables, you have to overwrite the whole dict, or else only the single overwritten will be actually used. So for example if you want to change the IPv4 traffic forwarding variable to 1, you must pass the whole dict like this:

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

          # Disable IPv6 traffic forwarding.
          net.ipv6.conf.all.forwarding: 0

          # ignore RAs on Ipv6.
          net.ipv6.conf.all.accept_ra: 0
          net.ipv6.conf.default.accept_ra: 0

          # Enable RFC-recommended source validation feature.
          net.ipv4.conf.all.rp_filter: 1
          net.ipv4.conf.default.rp_filter: 1

          # Reduce the surface on SMURF attacks.
          # Make sure to ignore ECHO broadcasts, which are only required in broad network analysis.
          net.ipv4.icmp_echo_ignore_broadcasts: 1

          # There is no reason to accept bogus error responses from ICMP, so ignore them instead.
          net.ipv4.icmp_ignore_bogus_error_responses: 1

          # Limit the amount of traffic the system uses for ICMP.
          net.ipv4.icmp_ratelimit: 100

          # Adjust the ICMP ratelimit to include ping, dst unreachable,
          # source quench, ime exceed, param problem, timestamp reply, information reply
          net.ipv4.icmp_ratemask: 88089

          # Disable IPv6
          net.ipv6.conf.all.disable_ipv6: 1

          # Protect against wrapping sequence numbers at gigabit speeds
          net.ipv4.tcp_timestamps: 0

          # Define restriction level for announcing the local source IP
          net.ipv4.conf.all.arp_ignore: 1

          # Define mode for sending replies in response to
          # received ARP requests that resolve local target IP addresses
          net.ipv4.conf.all.arp_announce: 2

          # RFC 1337 fix F1
          net.ipv4.tcp_rfc1337: 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.

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-1204

# test on all machines
bundle exec kitchen test

# for development
bundle exec kitchen create default-ubuntu-1204
bundle exec kitchen converge default-ubuntu-1204

Testing with Virtualbox

# fast test on one machine
KITCHEN_YAML=".kitchen.vagrant.yml" bundle exec kitchen test default-ubuntu-1204

# 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-1204
KITCHEN_YAML=".kitchen.vagrant.yml" bundle exec kitchen converge default-ubuntu-1204

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 sebastian.gumprich@38.de

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.