Server hardening

https://www.debian.org/doc/manuals/securing-debian-howto/

https://www.reddit.com/r/netsec/comments/ikkey/linux_server_hardening/?sort=top

https://www.thomas-krenn.com/de/wiki/Absicherung_eines_Debian_Servers

First minutes

The first steps after installing a new server to make sure nobody can capture it and use it in a way it was not intended. Make sure you work as fast and correct as possible until you reach BREAKTIME. That should not consume too much time and then you can think about what you want to install afterwards.

Create a new user with sudo rights

Create new User (at the server)

adduser sammy

Give sudo-rights (at the server)

usermod -aG sudo sammy

Generate SSH key (at own computer)

ssh-keygen

Copy the public key to server (at own computer)

ssh-copy-id sammy@your_server_ip

Test login

ssh sammy@serverip -p PORT

Configure SSH

sudo nano /etc/ssh/sshd_config

Disable root login: PermitRootLogin no Disable password login: ChallengeResponseAuthentication no or or PasswordAuthentication no Don't allow empty passwords: PermitEmptyPasswords no

change SSH Port

It's security by obscurity and not actually needed. It will reduce the amount of automated scans that reach your ssh-port but is not really something to secure the server. Just to keep your log files clear.

restart sshd

sudo systemctl restart sshd

Install fail2ban

sudo apt install fail2ban

sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local

and configure (1 short-lock for 24 hours, one for 1 week block)

https://www.booleanworld.com/protecting-ssh-fail2ban/

https://blog.shanock.com/fail2ban-increased-ban-times-for-repeat-offenders/

sudo nano /etc/fail2ban/jail.local

#
# JAILS
#
#
# SSH servers
#
[sshd]
# To use more aggressive sshd modes set filter parameter "mode" in jail.local:
# normal (default), ddos, extra or aggressive (combines all).
# See "tests/files/logs/sshd" or "filter.d/sshd.conf" for usage example and details.
mode = normal
port = ssh
logpath = %(sshd_log)s
backend = %(sshd_backend)s
# input by stefan
# one day
findtime = 5400 ;1.5 hours
maxretry = 5
bantime = 86400 ;1 day
# input by stefan, longterm ban
# 30 attempts over 3 days result in a 1 week ban
[sshlongterm2]
port = ssh
logpath = %(sshd_log)s
banaction = iptables-multiport
findtime = 259200 ;3 days
maxretry = 10
bantime = 604800 ;1 week
enabled = true
filter = sshd
[sshlongterm3]
enabled = true
filter = sshd
findtime = 15552000 ;6 months
maxretry = 15
bantime = 2592000 ;1 month
logpath = %(sshd_log)s
banaction = iptables-multiport

Check with tail

tail -10f /var/log/fail2ban.log

Update

sudo apt update && sudo apt upgrade

Install and configure UFW

Install und enable UFW and allow only SSH default [or Enable UFW and disable all inbound traffic from eth0 on all ports except SSH from my local IP (temporary, eventually I allow SSH globally due to potential for IP changes) and disable all outbound traffic except for port 80.] and for hosted websites port 80 and if you intend to use letsencrypt or somethinglike that port 443 too.

Important commands for UFW

ufw allow APPLICATION
ufw enable
ufw disable
ufw status

Important ports for the first use

ufw allow ssh
ufw allow http
ufw allow https

BREAKTIME

Pause, drink a cup of coffee, think about what you are going to do next and plan a little bit. The server now has some basic security.

After installing

Installing Tools

Tools

Install tools you want(vim, tmux, htop, nmap, sysstat, net-tools)

Mailserver

Install and configure mailserver (postfix with s-nail?) for automated messages from unattended upgrades or from other services.

Unattended Upgrades

Automatically just updates security-relevant updates. Can also update all updates, if you want. Can also send autmated messages if a mailserver is installed. A sugestion is to send on every update at first and change the setting later to “justOnError” in /etc/apt/apt.conf.d/50unattended-upgrades (multiple recipients separated with a komma)

Logrotate

Configure logrotate to rotate with dates instead of rolling numbers (easier for archive/backup) https://linoxide.com/linux-how-to/setup-log-rotation-logrotate-ubuntu/

Logwatch

daily mail set up

Time-Related

Configure time-related stuff (tzdata, install ntp, setting the time zone to UTC)

Disable unrequired services

Disable any and all services that are not required for the purpose of the box, bind others to localhost, unless they need to listen on public interfaces. This reduces attack vectors.

Check server

https://www.ssllabs.com/ssltest/analyze.html

Further hardening

AppArmor / SELinux

AppArmor (Ubuntu, Debian) or SeLinux (Fedora, CentOS, GenToo, OpenSUSE, possible to install on Ubuntu and Debian)

https://help.ubuntu.com/community/AppArmor

https://www.kuketz-blog.de/apparmor-linux-haerten-teil3/

su and sudo

Deactivate sudo for your account, check if login for root via ssh is deactivated

As for people telling you to sudo everything, I'm inclined to say “nah” I don't enable sudo on internet-facing machines. I use a strong password for root and su over to the account when I need to. No reason to hand over root access to someone who got into my user account.

I don't see how you consider su over sudo to be lazy. The default, “add user to wheel, enable sudo” is pretty garbage. If your user credentials are compromised, so is root. That's like advocating to add a user to the docker group on a container host. No one aside from myself has advocated for privilege separation or the use of strong ACLs/group policies.

The cult of “sudo all the things” is irresponsible. If you need root privileges, use root. Everything else should be covered under group policy.

Stuff

To integrate later

DOD STIG checklists

https://www.cisecurity.org/cis-benchmarks/

https://www.nsa.gov/ia/mitigation_guidance/security_configuration_guides/ (Check for new link!)

Centers for Internet Security config standards

http://greenfly.org/talks/security/simple_hardening.html

https://www.cyberciti.biz/tips/linux-security.html

https://linux-audit.com/ubuntu-server-hardening-guide-quick-and-secure/

Worth taking a look at

https://github.com/n1trux/awesome-sysadmin