Hardening Ubuntu. Systemd edition.

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

Tested on 18.04 Bionic Beaver, 18.10 Cosmic Cuttlefish and Ubuntu 19.04 Disco Dingo (development branch).

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.

If you’re using Ansible, a playbook with most of the above functions implemented is available in my Ansible repository konstruktoid/ansible-role-hardening.

Note	This is a constant work in progress. Make sure you understand what it does. Read the code.

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)

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

Login, set a Grub2 password, configure and run ubuntu.sh

Do not add any packages.
Log in.
Select a Grub2 password (using grub-mkpasswd-pbkdf2).
Download the script using git clone https://github.com/konstruktoid/hardening.git.
Change the configuration options in the ubuntu.cfg file and last but not least run the script, sudo bash ubuntu.sh.

Configuration options

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

# 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'
DEFAULTGRUB='/etc/default/grub'
DISABLEMNT='/etc/modprobe.d/disablemnt.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'
RESOLVEDCONF='/etc/systemd/resolved.conf'
RKHUNTERCONF='/etc/default/rkhunter'
SECURITYACCESS='/etc/security/access.conf'
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'

1. The IP addresses that will be able to connect with SSH, separated by spaces.

2. Which group the users have to be member of in order to acess via SSH, separated by spaces.

3. Stricter sysctl settings.

4. Auditd failure mode. 0=silent 1=printk 2=panic.

5. Auditd rules.

6. Logrotate settings.

7. NTP server pool.

8. Add a specific time zone or use the system default by leaving it empty.

9. If you want all the details or not.

10. Let the script guess the FW_ADMIN and SSH_GRPS settings.

11. 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

RHEL-07-040520

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

03_disablenet

CCE-26828-4, CCE-27106-4

Disable dccp sctp rds tipc protocols.

04_disablemnt

CCE-80137-3, CCE-80138-1, CCE-80139-9, CCE-80140-7, CCE-80141-5, CCE-80142-3, CCE-80143-1, UBTU-16-010070

Disable cramfs freevxfs jffs2 hfs hfsplus squashfs 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.

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

CCE-27078-5

Undo prelinking, and remove prelink package.

10_aptget

CCE-26895-3, UBTU-16-010010, UBTU-16-010560, UBTU-16-010570

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

11_hosts

V-72315

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

12_logindefs

CCE-80205-8, UBTU-16-010150, UBTU-16-010170, UBTU-16-010190, UBTU-16-010210, UBTU-16-010220, UBTU-16-010640

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

13_sysctl

Update $SYSCTL with $SYSCTL_CONF.

14_limits

CCE-80169-6, V-72049

Set hard and soft limits.

15_adduser

UBTU-16-010280

Set /bin/false as default shell when adding users.

16_rootaccess

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

17_packages

UBTU-16-010050, UBTU-16-010500, UBTU-16-010600

Installs acct aide-common apparmor-profiles apparmor-utils auditd debsums haveged libpam-apparmor libpam-cracklib libpam-tmpdir openssh-server postfix rkhunter vlock.

Removes avahi* beep popularity-contest rsh* talk* telnet* tftp* yp-tools ypbind xinetd.

18_sshdconfig

CCE-27471-2, CCE-27082-7, CCE-27433-2, CCE-27314-4, CCE-27363-1, CCE-27413-4, CCE-80222-3, CCE-80223-1, CCE-80225-6, CCE-80224-9, CCE-27445-6, UBTU-16-030200, UBTU-16-030210, UBTU-16-030270, UBTU-16-030350

Configure the OpenSSH-daemon.

19_password

UBTU-16-010090, UBTU-16-010100, UBTU-16-010110, UBTU-16-010120, UBTU-16-010120, UBTU-16-010130, UBTU-16-010140, UBTU-16-010180, UBTU-16-010230, UBTU-16-010240, UBTU-16-010250, UBTU-16-010290, UBTU-16-010320, UBTU-16-010340

Configure pam_cracklib.so and pam_tally2.so.

20_cron

CCE-27323-5, CCE-80345-2

Allow root to use cron. Mask atd.

21_ctraltdel

CCE-27511-5, UBTU-16-010630

Disable Ctrl-alt-delete.

22_auditd

CCE-27407-6, UBTU-16-020000

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

23_disablemod

CCE-27327-6, CCE-27277-3, UBTU-16-010580

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

24_aide

CCE-27096-7, UBTU-16-020000, UBTU-16-020010

Configure aide.

25_rhosts

CCE-27406-8

Remove hosts.equiv and .rhosts.

26_users

UBTU-16-010650

Remove games gnats irc list news sync uucp users.

27_suid

Remove suid bits from /bin/fusermount /bin/mount /bin/ping /bin/ping6 /bin/su /bin/umount /usr/bin/bsd-write /usr/bin/chage /usr/bin/chfn /usr/bin/chsh /usr/bin/mlocate /usr/bin/mtr /usr/bin/newgrp /usr/bin/pkexec /usr/bin/traceroute6.iputils /usr/bin/wall /usr/sbin/pppd.

28_umask

CCE-80202-5, UBTU-16-010060

Set bash and /etc/profile umask.

29_apparmor

UBTU-16-010600, UBTU-16-010610, UBTU-16-010620

Enforce present apparmor profiles.

30_path

UBTU-16-010780

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

Mask apport.service and disable apport.

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.

98_systemddelta

If verbose, show systemd-delta.

99_reboot

Print if a reboot is required.

Function execution order

f_pre
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_logindefs
f_sysctl
f_limitsconf
f_adduser
f_rootaccess
f_package_remove
f_package_install
f_coredump
f_usbguard
f_postfix
f_apport
f_motdnews
f_rkhunter
f_sshdconfig
f_password
f_cron
f_ctrlaltdel
f_auditd
f_aide
f_rhosts
f_users
f_lockroot
f_aptget_clean
f_suid
f_restrictcompilers
f_umask
f_path
f_aa_enforce
f_aide_post
f_aide_timer
f_aptget_noexec
f_systemddelta
f_checkreboot

Tests

There are approximately 450 Bats tests for most of the above settings available in the tests directory.

git clone https://github.com/konstruktoid/hardening.git
cd tests/
sudo bats .

Test automation

Running bash ./runTests.sh will use Vagrant to run all above tests and Lynis on all supported Ubuntu versions.

Structure

.
├── LICENSE
├── README.adoc
├── Vagrantfile
├── action-shellcheck
│   ├── Dockerfile
│   ├── README.md
│   └── entrypoint.sh
├── checkScore.sh
├── config
│   ├── aidecheck.service
│   ├── aidecheck.timer
│   ├── initpath.sh
│   └── tmp.mount
├── createPartitions.sh
├── misc
│   ├── audit-aggressive.rules
│   ├── audit-base.rules
│   ├── audit-docker.rules
│   ├── audit.footer
│   ├── audit.header
│   ├── auditgenerator.sh
│   ├── fdcount.sh
│   ├── logrotate.conf
│   ├── proc_check.sh
│   ├── sysctl.conf
│   └── systemd_scan.sh
├── renovate.json
├── runTests.sh
├── scripts
│   ├── 01_pre
│   ├── 02_ufw
│   ├── 03_disablenet
│   ├── 04_disablefs
│   ├── 05_systemdconf
│   ├── 06_journalctl
│   ├── 07_timesyncd
│   ├── 08_fstab
│   ├── 09_prelink
│   ├── 10_aptget
│   ├── 11_hosts
│   ├── 12_logindefs
│   ├── 13_sysctl
│   ├── 14_limits
│   ├── 15_adduser
│   ├── 16_rootaccess
│   ├── 17_packages
│   ├── 18_sshdconfig
│   ├── 19_password
│   ├── 20_cron
│   ├── 21_ctraltdel
│   ├── 22_auditd
│   ├── 23_disablemod
│   ├── 24_aide
│   ├── 25_rhosts
│   ├── 26_users
│   ├── 27_suid
│   ├── 28_umask
│   ├── 29_apparmor
│   ├── 30_path
│   ├── 31_logindconf
│   ├── 32_resolvedconf
│   ├── 33_rkhunter
│   ├── 34_issue
│   ├── 35_apport
│   ├── 36_lockroot
│   ├── 37_coredump
│   ├── 38_postfix
│   ├── 39_motdnews
│   ├── 40_usbguard
│   ├── 41_compilers
│   ├── 98_systemddelta
│   └── 99_reboot
├── systemd.adoc
├── tests
│   ├── 01_pre.bats
│   ├── 02_ufw.bats
│   ├── 03_disablenet.bats
│   ├── 04_disablefs.bats
│   ├── 05_systemdconf.bats
│   ├── 06_journalctl.bats
│   ├── 07_timesyncd.bats
│   ├── 08_fstab.bats
│   ├── 10_aptget.bats
│   ├── 11_hosts.bats
│   ├── 12_logindefs.bats
│   ├── 13_sysctl.bats
│   ├── 14_limits.bats
│   ├── 15_adduser.bats
│   ├── 16_rootaccess.bats
│   ├── 17_packages.bats
│   ├── 18_sshd.bats
│   ├── 19_password.bats
│   ├── 20_cron.bats
│   ├── 21_ctrlaltdel.bats
│   ├── 22_auditd.bats
│   ├── 23_disablemod.bats
│   ├── 24_aide.bats
│   ├── 26_users.bats
│   ├── 27_suid.bats
│   ├── 28_umask.bats
│   ├── 29_apparmor.bats
│   ├── 31_logindconf.bats
│   ├── 32_resolvedconf.bats
│   ├── 33_rkhunter.bats
│   ├── 35_apport.bats
│   ├── 36_lockroot.bats
│   ├── 37_coredump.bats
│   ├── 38_postfix.bats
│   ├── 39_motdnews.bats
│   ├── 40_usbguard.bats
│   ├── 41_compilers.bats
│   ├── 99_misc.bats
│   └── test_helper.bash
├── ubuntu.cfg
└── ubuntu.sh

Recommended reading

CIS Distribution Independent Linux Benchmark v1.0.0
Red Hat Enterprise Linux 7 Security Technical Implementation Guide Version: 1 Release: 4
Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide Version: 1 Release: 1
CIS Ubuntu Linux Benchmarks
https://wiki.ubuntu.com/Security/Features
https://help.ubuntu.com/community/StricterDefaults
EUD Security Guidance: Ubuntu 18.04 LTS