Here is a list of things I do to secure my server.

1. Turn on UFW (sudo ufw enable) and then only allow ports that are actually used. (sudo ufw allow 80)
2. Make sure MySQL only allows connections from localhost.
3. Enable TLS on mail services. Even if it's a self-signed cert. You don't want passwords sent in the clear.
4. Install ssh bruteforce blockers like denyhosts or fail2ban. (sudo apt-get install denyhosts)
5. Look into making ssh key-based logins only.
6. Learn AppArmor. If you use fairly vanilla configurations, then it's extremely easy. Just make sure it's turned on. It will help reduce zero-day exploits.
7. Depending on physical access to the server, you may even want to look at encrypting the data on the harddisk.
8. Follow other recommendations in https://help.ubuntu.com/18.04/serverguide/security.html.
9. Never trust your users. If you are having multiple users with access to the system, lock them down. If you have to give them sudo access, give them only what they need.
10. Use common sense. Think real hard about how you'd get in if you were ever locked out. Then close those holes.

A few more things to consider. Most people forget about physical access. All the software configurations in the world don't mean anything if I can physically walk in with a LiveCD and steal your data. Beware of social engineering. Ask questions to verify who is on the phone and make sure they have the authorization to make the request they are making.

You can read up more about this subject on https://help.ubuntu.com/18.04/serverguide/index.html and pay special attention to https://help.ubuntu.com/18.04/serverguide/security.html.

Since you said this is web-hosting-server... I would like to share my best practices and experience of 5 long years in the web-hosting line.

1. From my past experiences, rather than going into configuration hell straight away, you should first assemble the low hanging grapes of security as indicated on the given article.

2. Since you are having LAMP, thus you must be very cautious bout PHP and its php.ini settings. This is a good link for securing PHP. PHP has super powers which may become security loop when not configured properly.

3. You may use a cron job to check when your files were modified without your permission and possibly hacked; using this cron job. I prefer Notepad++ to compare the cron results (directly download the cron email from your web server and open in Notepad++).

4. If you want to install some SEM, then cPanel is best preferred (however paid). Webmin and zpanel are very good free alternatives. Webmin is better for it atleast uses self signed certificates and adds security.

5. If you want something to work right out of the box then you may go for Turnkey Linux. It is based on Ubuntu, extremely easy to implement and flexible to your needs. With very little effort you get security out of the box. This is their LAMP stack. I personally use and prefer this only.

6. If you are starting from scratches, then you may also install ISPconfig3. Instruction Here.

7. you may test your security by trying to penetrate your security using Back-Track-Linux.

8. keep complex long and random passwords. Dont store them on PC. write them down. Use a live CD to access these logins.

9. get a brute force protection software like fail2ban.

10. Dont run those daemons which you don't need.

11. Block all the unnecessary ports. be extremely careful with SSH port (22).

12. Get yourself with a static IP on the system through which you gonna manage the server. Make most of the things IP block and only allow your particular IP to access those configuration places like port 22.

In the end of the day... work with utter piece of mind, don't get emotional with the install and applying common sense takes you far beyond.

**My heartiest best wishes to you. good luck.**

Secure shared memory

/dev/shm can be used in an attack against a running service, such as httpd. Modify /etc/fstab to make it more secure.

Open a Terminal Window and enter the following :

sudo vi /etc/fstab

Add the following line and save. You will need to reboot for this setting to take effect :

tmpfs     /dev/shm     tmpfs     defaults,noexec,nosuid     0     0

Harden network with sysctl settings

The /etc/sysctl.conf file contain all the sysctl settings. Prevent source routing of incoming packets and log malformed IP's enter the following in a terminal window

sudo vi /etc/sysctl.conf

Edit the /etc/sysctl.conf file and un-comment or add the following lines :

# IP Spoofing protection
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1

# Ignore ICMP broadcast requests
net.ipv4.icmp_echo_ignore_broadcasts = 1

# Disable source packet routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv6.conf.all.accept_source_route = 0 
net.ipv4.conf.default.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0

# Ignore send redirects
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0

# Block SYN attacks
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_max_syn_backlog = 2048
net.ipv4.tcp_synack_retries = 2
net.ipv4.tcp_syn_retries = 5

# Log Martians
net.ipv4.conf.all.log_martians = 1
net.ipv4.icmp_ignore_bogus_error_responses = 1

# Ignore ICMP redirects
net.ipv4.conf.all.accept_redirects = 0
net.ipv6.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0 
net.ipv6.conf.default.accept_redirects = 0

# Ignore Directed pings
net.ipv4.icmp_echo_ignore_all = 1

To reload sysctl with the latest changes, enter:

sudo sysctl -p

Prevent IP Spoofing

Open a Terminal and enter the following :

sudo vi /etc/host.conf

Add or edit the following lines :

order bind,hosts
nospoof on

Harden PHP for security

Edit the php.ini file :

sudo vi /etc/php5/apache2/php.ini

Add or edit the following lines :

disable_functions = exec,system,shell_exec,passthru
register_globals = Off
expose_php = Off
magic_quotes_gpc = On

Web Application Firewall - ModSecurity

http://www.thefanclub.co.za/how-to/how-install-apache2-modsecurity-and-modevasive-ubuntu-1204-lts-server

Protect from DDOS (Denial of Service) attacks - ModEvasive

http://www.thefanclub.co.za/how-to/how-install-apache2-modsecurity-and-modevasive-ubuntu-1204-lts-server

Scan logs and ban suspicious hosts - DenyHosts and Fail2Ban

@DenyHosts

DenyHosts is a python program that automatically blocks SSH attacks by adding entries to /etc/hosts.deny. DenyHosts will also inform Linux administrators about offending hosts, attacked users and suspicious logins.

Open a Terminal and enter the following :

sudo apt-get install denyhosts

After installation edit the configuration file /etc/denyhosts.conf and change the email, and other settings as required.

To edit the admin email settings open a terminal window and enter:

sudo vi /etc/denyhosts.conf

Change the following values as required on your server :

ADMIN_EMAIL = root@localhost
SMTP_HOST = localhost
SMTP_PORT = 25
#SMTP_USERNAME=foo
#SMTP_PASSWORD=bar
SMTP_FROM = DenyHosts nobody@localhost
#SYSLOG_REPORT=YES 

@ Fail2Ban

Fail2ban is more advanced than DenyHosts as it extends the log monitoring to other services including SSH, Apache, Courier, FTP, and more.

Fail2ban scans log files and bans IPs that show the malicious signs -- too many password failures, seeking for exploits, etc.

Generally Fail2Ban then used to update firewall rules to reject the IP addresses for a specified amount of time, although any arbitrary other action could also be configured. Out of the box Fail2Ban comes with filters for various services (apache, courier, ftp, ssh, etc).

Open a Terminal and enter the following :

sudo apt-get install fail2ban

After installation edit the configuration file /etc/fail2ban/jail.local and create the filter rules as required.

To edit the settings open a terminal window and enter:

sudo vi /etc/fail2ban/jail.conf

Activate all the services you would like fail2ban to monitor by changing enabled = false to *enabled = true*

For example if you would like to enable the SSH monitoring and banning jail, find the line below and change enabled from false to true. Thats it.

[ssh]

enabled  = true
port     = ssh
filter   = sshd
logpath  = /var/log/auth.log
maxretry = 3

If you would like to receive emails from Fail2Ban if hosts are banned change the following line to your email address.

destemail = root@localhost

and change the following line from :

action = %(action_)s

to:

action = %(action_mwl)s

You can also create rule filters for the various services that you would like fail2ban to monitor that is not supplied by default.

sudo vi /etc/fail2ban/jail.local

Good instructions on how to configure fail2ban and create the various filters can be found on HowtoForge - click here for an example

When done with the configuration of Fail2Ban restart the service with :

sudo /etc/init.d/fail2ban restart

You can also check the status with.

sudo fail2ban-client status

Check for rootkits - RKHunter and CHKRootKit.

Both RKHunter and CHKRootkit basically do the same thing - check your system for rootkits. No harm in using both.

Open a Terminal and enter the following :

sudo apt-get install rkhunter chkrootkit

To run chkrootkit open a terminal window and enter :

sudo chkrootkit

To update and run RKHunter. Open a Terminal and enter the following

sudo rkhunter --update
sudo rkhunter --propupd
sudo rkhunter --check

Scan open ports - Nmap

Nmap ("Network Mapper") is a free and open source utility for network discovery and security auditing.

Open a Terminal and enter the following :

sudo apt-get install nmap

Scan your system for open ports with :

nmap -v -sT localhost

SYN scanning with the following :

sudo nmap -v -sS localhost

Analyse system LOG files - LogWatch

Logwatch is a customizable log analysis system. Logwatch parses through your system's logs and creates a report analyzing areas that you specify. Logwatch is easy to use and will work right out of the package on most systems.

Open a Terminal and enter the following :

sudo apt-get install logwatch libdate-manip-perl

To view logwatch output use less :

sudo logwatch | less

To email a logwatch report for the past 7 days to an email address, enter the following and replace [email protected] with the required email. :

sudo logwatch --mailto [email protected] --output mail --format html --range 'between -7 days and today' 

Audit your system security - Tiger.

Tiger is a security tool that can be use both as a security audit and intrusion detection system.

Open a Terminal and enter the following :

sudo apt-get install tiger

To run tiger enter :

sudo tiger

All Tiger output can be found in the /var/log/tiger

To view the tiger security reports, open a Terminal and enter the following :

sudo less /var/log/tiger/security.report.*

For More Help

Make use of the Bastille Linux project.

It provides an interactive tool to perform additional security hardening measures to increase the over-all security, and decrease the susceptibility of compromise for your Ubuntu system (from Bastille Linux).

It offers an assessment and reporting functionality, so that it can tell you what parts of the system aren't locked down. It examines the system in a read-only fashion, reporting on the status of each of its hardening items. For example, Bastille might check whether the DNS server is locked in a chroot prison, whether telnet is turned off, or even if passwords are required to be a good length. You can take a look at a Web-only demo of this through this link (more info).

You can have preview of the Web (only) demo here.

Use nmap on all interfaces on the machine, so you know what services you run on your machine. This is an essential tool for security.

Remove all services you don't need on your external interfaces. You can configure MySQL to only listen on specific interfaces, like localhost.

Use ufw to protect your SSH service (and possible others) so that it doesn't allow too many (failed) connections per minute from same machine. That will make brute force attacks harder. To change port number isn't that usefull, just obscurity, no security.

Be restrictive with the number of accounts on your machine. Also don't install more packages/programs than you actually uses. Only install X11-clients, not a X11-server.

Only allow ssh-login to the machine with digital certificates, no password. That will also make brute force attacks hard/impossible.

I would also consult the CIS Debian Benchmarks document and it has a significant number of procedures and processes for hardening the operating system that will apply to Ubuntu since it's a derivative of Debian. I would also consult:

• Securing Debian Howto
• Debian Hardening Walkthrough
• Hardening The Linux Kernel With Grsecurity (Debian)

Security always comes with a price. Setting some realistic boundaries will help you in getting your goals. I would consider the following aspects:

• Against what are you protecting yourself (which type of villain, what is his budget)?
• What are your attack vectors?

Checking all the links that are posted here, I think this one should be added. It goes into detail about not only how to setup your software, but also to think about the security plan. As a plus, every command to execute is explained with a source to it.

Securing an Ubuntu Webserver on Xenial 16.04

I made a post about this not long ago on how to secure ubuntu 16.04-18.04. These steps include:

Replace Password Login With Authorized keys Install a Firewall on Your Linux Server

and some more. https://hostup.org/blog/how-to-secure-a-ubuntu-linux-server-in-3-simple-steps/

In addition to all that already said, you could use apt install snoopy and send all your syslog-logfiles to an external logserver.

This way you can help that an attacker, if he succeeds, does not go unnoticed. Remote logs mean, an attacker has to hack another system to hide his tracks.

This is helpfull to do forensics on an already compromised system.