Hardening Ubuntu. Systemd edition.

A quick way to make a Ubuntu server a bit more secure.

Tested on Ubuntu 20.04 Focal Fossa and Ubuntu 21.10 Impish Indri.

Systemd required.

If you’re just interested in the security focused systemd configuration, it’s available as a separate document.

If you’re interested in testing your host settings, you’ll find the instructions here.

Note	This is a constant work in progress. Make sure you understand what it does. Read the code and do not run this script without first testing in a non-operational environment.

When possible, use the newly installed and configured system as a reference, or golden, image. Use that image as a baseline installation media and ensure that any future installation comply with benchmarks and policies using a configuration management tool, e.g Ansible or Puppet.

Packer template and Ansible playbook

A Packer template is available in the konstruktoid/hardening-geniso repository.

An Ansible playbook is available in the konstruktoid/ansible-role-hardening repository.

Howto

Start the installation of the server.
Pick language, keyboard layout, timezone and so on as you usually would.

Partition the system

/
/boot (rw)
/home (rw,nosuid,nodev)
swap
/var
/var/log (rw,nosuid,nodev,noexec)
/var/log/audit (rw,nosuid,nodev,noexec)
/var/tmp (rw,noexec,nodev,nosuid)

Note that /tmp will be added automatically by the script.

Do not add any packages.
Log in.
Select a Grub2 password with grub-mkpasswd-pbkdf2.
Download the script: git clone https://github.com/konstruktoid/hardening.git.
Change the configuration options in the ubuntu.cfg file.
Run the script: sudo bash ubuntu.sh.
Reboot.

Configuration options

FW_ADMIN='127.0.0.1' // (1)
SSH_GRPS='sudo' // (2)
SSH_PORT='22' // (3)
SYSCTL_CONF='./misc/sysctl.conf' // (4)
AUDITD_MODE='1' // (5)
AUDITD_RULES='./misc/audit-base.rules ./misc/audit-aggressive.rules ./misc/audit-docker.rules' // (6)
LOGROTATE_CONF='./misc/logrotate.conf' // (7)
NTPSERVERPOOL='0.ubuntu.pool.ntp.org 1.ubuntu.pool.ntp.org 2.ubuntu.pool.ntp.org 3.ubuntu.pool.ntp.org pool.ntp.org' // (8)
TIMEDATECTL='' // (9)
VERBOSE='N' // (10)
AUTOFILL='N' // (11)
ADMINEMAIL="root@localhost" // (12)
CHANGEME='' // (13)

# Configuration files
ADDUSER='/etc/adduser.conf'
AUDITDCONF='/etc/audit/auditd.conf'
AUDITRULES='/etc/audit/rules.d/hardening.rules'
COMMONPASSWD='/etc/pam.d/common-password'
COMMONACCOUNT='/etc/pam.d/common-account'
COMMONAUTH='/etc/pam.d/common-auth'
COREDUMPCONF='/etc/systemd/coredump.conf'
DEFAULTGRUB='/etc/default/grub.d'
DISABLEFS='/etc/modprobe.d/disablefs.conf'
DISABLEMOD='/etc/modprobe.d/disablemod.conf'
DISABLENET='/etc/modprobe.d/disablenet.conf'
JOURNALDCONF='/etc/systemd/journald.conf'
LIMITSCONF='/etc/security/limits.conf'
LOGINDCONF='/etc/systemd/logind.conf'
LOGINDEFS='/etc/login.defs'
LOGROTATE='/etc/logrotate.conf'
PAMLOGIN='/etc/pam.d/login'
PSADCONF='/etc/psad/psad.conf'
PSADDL='/etc/psad/auto_dl'
RESOLVEDCONF='/etc/systemd/resolved.conf'
RKHUNTERCONF='/etc/default/rkhunter'
RSYSLOGCONF='/etc/rsyslog.conf'
SECURITYACCESS='/etc/security/access.conf'
SSHFILE='/etc/ssh/ssh_config'
SSHDFILE='/etc/ssh/sshd_config'
SYSCTL='/etc/sysctl.conf'
SYSTEMCONF='/etc/systemd/system.conf'
TIMESYNCD='/etc/systemd/timesyncd.conf'
UFWDEFAULT='/etc/default/ufw'
USERADD='/etc/default/useradd'
USERCONF='/etc/systemd/user.conf'

The IP addresses that will be able to connect with SSH, separated by spaces.
Which group the users have to be member of in order to acess via SSH, separated by spaces.
Configure SSH port.
Stricter sysctl settings.
Auditd failure mode. 0=silent 1=printk 2=panic.
Auditd rules.
Logrotate settings.
NTP server pool.
Add a specific time zone or use the system default by leaving it empty.
If you want all the details or not.
Let the script guess the FW_ADMIN and SSH_GRPS settings.
Add a valid email address, so PSAD can send notifications.
Add something just to verify that you actually glanced the code.

Functions

Function list

01_pre

Setup script, sets APT flags and permission checks.

02_firewall

Enable ufw, use /etc/sysctl.conf, prepare to psad, and allow port 22 from $FW_ADMIN.

03_disablenet

Disable dccp sctp rds tipc protocols.

04_disablemnt

Disable cramfs freevxfs jffs2 hfs hfsplus udf vfat file systems.

05_systemdconf

Disable coredumps and crash shells, set DefaultLimitNOFILE and DefaultLimitNPROC to 1024.

06_journalctl

Compress logs, forward to syslog and make log storage persistent. Ensure rsyslog writes logs with stricter permissions.

07_timesyncd

Add four NTP-servers with a latency < 50ms from $NTPSERVERPOOL.

08_fstab

Configure /tmp/ and /var/tmp/. Remove floppy drivers from /etc/fstab and add hidepid=2 to /proc.

09_prelink

Undo prelinking, and remove prelink package.

10_aptget

Configure dpkg and apt-get. apt-get update and upgrade.

11_hosts

/etc/hosts.allow and /etc/hosts.deny restrictions.

12_logindefs

Modify /etc/login.defs, e.g. UMASK, password age limits and SHA_CRYPT_MAX_ROUNDS.

13_sysctl

Update $SYSCTL with $SYSCTL_CONF.

14_limits

Set hard and soft limits.

15_adduser

Configure useradd and adduser to set /bin/false as default shell, home directory permissions to 0750 and lock users 30 days after password expires.

16_rootaccess

Limit /etc/securetty to console, and root from 127.0.0.1 in /etc/security/access.conf.

17_packages

Installs acct aide-common apparmor-profiles apparmor-utils auditd audispd-plugins debsums gnupg2 haveged libpam-apparmor libpam-pwquality libpam-tmpdir needrestart openssh-server postfix rkhunter sysstat systemd-coredump tcpd psad update-notifier-common vlock.

Removes apport* autofs avahi* beep git pastebinit popularity-contest rsh* rsync talk* telnet* tftp* whoopsie xinetd yp-tools ypbind.

18_sshdconfig

Configure the OpenSSH-daemon.

19_password

Configure pam_pwquality.so and pam_tally2.so.

20_cron

Allow root to use cron. Mask atd.

21_ctraltdel

Disable Ctrl-alt-delete.

22_auditd

Configure auditd, use $AUDITD_RULES and set failure mode $AUDITD_MODE.

23_disablemod

Disable bluetooth bnep btusb cpia2 firewire-core floppy n_hdlc net-pf-31 pcspkr soundcore thunderbolt usb-midi usb-storage uvcvideo v4l2_common kernel modules.

Note that disabling the usb-storage will disable any usage of USB storage devices, if such devices are needed USBGuard should be configured accordingly.

24_aide

Configure aide.

25_rhosts

Remove hosts.equiv and .rhosts.

26_users

Remove games gnats irc list news sync uucp users.

27_suid

Remove suid bits from the executables listed in this document.

28_umask

Set bash and /etc/profile umask.

29_apparmor

Enforce present apparmor profiles.

30_path

Set root path to /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin, and user path to /usr/local/bin:/usr/bin:/bin.

31_logindconf

Configure systemd/logind.conf and use KillUserProcesses.

32_resolvedconf

Configure systemd/resolved.conf.

33_rkhunter

Configure rkhunter.

34_issue

Update /etc/issue /etc/issue.net /etc/motd.

35_apport

Disable apport, ubuntu-report and popularity-contest.

36_lockroot

Lock the root user account.

37_coredump

Disable coredumps with systemd/coredump.conf.

38_postfix

Disable the VRFY command, configure smtpd_banner, smtpd_client_restrictions and inet_interfaces.

39_motdnews

Disable motd-news.

40_usbguard

Install and configure usbguard.

41_compilers

Restrict compiler access.

42_kernel

Set lockdown=confidentiality if /sys/kernel/security/lockdown is present.

43_sudo

Configure sudo with use_pty, logfile, !visiblepw, !pwfeedback, passwd_timeout and timestamp_timeout.

Restrict su to the sudo group.

44_psad

Configure psad.

98_systemddelta

If verbose, show systemd-delta.

99_post

Ensure secureboot-db is installed, update grub and ensure strict permissions on boot files.

99_reboot

Print if a reboot is required.

Function execution order

f_pre
f_kernel
f_firewall
f_disablenet
f_disablefs
f_disablemod
f_systemdconf
f_resolvedconf
f_logindconf
f_journalctl
f_timesyncd
f_fstab
f_prelink
f_aptget_configure
f_aptget
f_hosts
f_issue
f_sudo
f_logindefs
f_sysctl
f_limitsconf
f_adduser
f_rootaccess
f_package_install
f_coredump
f_usbguard
f_postfix
f_apport
f_motdnews
f_rkhunter
f_sshconfig
f_sshdconfig
f_password
f_cron
f_ctrlaltdel
f_auditd
f_psad
f_aide
f_rhosts
f_users
f_lockroot
f_package_remove
f_suid
f_restrictcompilers
f_umask
f_path
f_aa_enforce
f_aide_post
f_aide_timer
f_aptget_noexec
f_aptget_clean
f_systemddelta
f_post
f_checkreboot

Tests

There are approximately 750 Bats tests for most of the above settings available in the tests directory.

sudo apt-get -y install bats
git clone https://github.com/konstruktoid/hardening.git
cd hardening/tests/
sudo bats .

Test automation using Vagrant

Running bash ./runTests.sh will use Vagrant to run all above tests and Lynis on all supported Ubuntu versions. The script will generate a file named TESTRESULTS.adoc.

Testing a host

Running bash ./runHostTests.sh, located in the tests directory, will generate a TESTRESULTS-<HOSTNAME>.adoc report.

Issues: snapd

In order to use snapd you will have to disable the kernel_lockdown setting, update grub, reboot the host and then reinstall snapd.

sudo sed -i 's/^/# /g' /etc/default/grub.d/99-hardening-lockdown.cfg
sudo update-grub
sudo reboot
sudo apt-get --assume-yes --reinstall install snapd

Contributing

Do you want to contribute? That’s great! Contributions are always welcome, no matter how large or small. If you found something odd, feel free to submit a new issue, improve the code by creating a pull request, or by sponsoring this project.

Logo by reallinfo.

damjankumin/hardening