Linux server security is on sufficient level from the moment you install the OS. And that’s great to know because… hackers never sleep! They’re kind of like digital vandals. Taking pleasure – and sometimes money too – as they inflict misery on random strangers all over the planet.
Anyone who looks after their own server appreciates the fact that Linux is highly secure right out the box. Naturally, it isn’t completely watertight. But it does do a better job of keeping you safe than most other operating systems.
Still, there are plenty of ways you can improve it further. So here are some practical ways how you can keep the evil hordes from the gates. It will probably help if you’ve tinkered under the hood of a web server before. But don’t think that you have to be a tech guru or anything like that.
Deactivate network ports when not in use
Leave a network port open and you might as well put out the welcome mat for hackers. To maintain web host security you can use the “netstat” command to inform you which network ports are currently open. And also which services are making use of them. This should close off another avenue of attack for hackers.
You also might want to set up “iptables” to deactivate open ports. Or simply use the “chkconfig” command to shut down services you won’t need. Firewalls like CSF let you automate the iptables rules, so you could just do that. If you use Plesk platform as your hosting management software – please pay attention to this article about Plesk ports.
The SSH port is usually 22, and that’s where hackers will expect to find it. To enhance Linux server security, change it to some other port number you’re not already using for another service. This way, you’ll be making it harder for the bad guys to inject malware into your server. To make the change, just go to /etc/ssh/sshd_config and enter the appropriate number.
Update Linux Software and Kernel
Half of the Linux security battle is keeping everything up to date because updates frequently add extra security features. Linux offers all the tools you need to do this, and upgrading between versions is simple too. Every time a new security update becomes available, you need to review it and install it as soon as you can. Again, you can use an RPM package manager like yum and/or apt-get and/or dpkg to handle this.
# yum update
# apt-get update && apt-get upgrade
It’s possible to set up RedHat / CentOS / Fedora Linux so that you get yum package update notifications sent to your email. This is great for Linux security and you can also apply all security updates using a cron job. Apticron can be used to send security mitigations under Debian / Ubuntu Linux. You can also use the apt-get command/apt command to configure unattended-upgrades for your Debian/Ubuntu Linux server:
$ sudo apt-get install unattended-upgrades apt-listchanges bsd-mailx
Reduce Redundant Software to Increase Linux Security
For greater Linux server security hardening It’s worth doing a spring clean (at any time of the year) on your installed web services. It’s easy for surplus apps to accumulate and you will probably find that you don’t need half of them. In the future, for better Linux server security try not to install software that you don’t need. It’s a simple and effective way to reduce potential security holes. Use an RPM package manager like yum or apt-get and/or dpkg to go through your installed software and remove any that you don’t need any more.
# yum list installed
# yum list packageName
# yum remove packageName
# dpkg --list
# dpkg --info packageName
# apt-get remove packageName
Turn off root logins to improve Linux server security
Linux servers the world over allow the use of “root” as a username. Knowing this, hackers will often try subverting web host security to discover your password before slithering inside. It’s because of this that you should not sign in as the root user. In fact, you really ought to remove it as an option, creating one more level of difficulty for hackers. And thus, stopping them from being able to get past your security with just a lucky guess.
So, all it takes is for you to create a separate username. Then use the “sudo” special access command to execute root level commands. Sudo is great because you can give it to any users you want to have admin commands, but not root access. Because you don’t want to compromise security by giving them both.
So you deactivate the root account, but before, check you’ve created and authorized your new user. Next, go to /etc/ssh/sshd_config in nano or vi, then locate the “PermitRootLogin” parameter. Change the default setting of “yes” to “no” and then save your changes.
GnuPG encryption for web host security
When data is on the move across your network, hackers will frequently attempt to compromise Linux server security by intercepting it. Always make sure anything going to and from your server has password encryption, certificates and keys. One way to do this is with an encryption tool like GnuPG. It uses a system of keys to ensure nobody can snoop on your info when in transit.
Change/boot to read-only
All files related to the kernel on a Linux server are in the “/boot” directory. The standard access level for the directory is “read-write”, but it’s a good idea to change it to “read-only”. This stops anyone from modifying your extremely important boot files.
Just edit the /etc/fstab file and add LABEL=/boot /boot ext2 defaults, rows 1 2 to the bottom. It is completely reversible, so you can make future changes to the kernel by changing it back to “read-write” mode. Then, once you’re done, you can revert back to “read only”.
A better password policy enhances Web Host Security
Passwords are always a security problem because humans are. People can’t be bothered to come up with a lot of different passwords – or maybe they can’t. So what happens? They use the same ones in different places. Or worse yet – combinations that are easy to remember, like “password” or “abcde”. Basically, a gift to hackers.
Make it a requirement for passwords to contain a mix of upper AND lower case letters, numbers, and symbols. You can enable password ageing to make users discard previous passwords at fixed intervals. Also think about banning old passwords, so once people use one, it’s gone forever. The “faillog” command lets you put a limit on the amount of failed login attempts allowed and lock user accounts. This is ideal to prevent brute force attacks.
So just use a strong password all the time
Passwords are your first line of defense, so make sure they’re strong. Many people don’t really know what a good password looks like. That it needs to be complex, but also long enough to make it the strongest it can be.
At admin level, you can help users by securing Plesk Obsidian and enforcing the use of strong passwords which expire after a fixed period. Users may not like it, but you need to make them understand that it saves them a lot of possible heartache.
So what are the ‘best practices’ when setting up passwords?
- Use passwords that are as long as you can manage
- Avoid words that appear in the dictionary (like “blue grapes”)
- Steer clear of number replacements that are easy to guess (like “h3ll0”)
- Don’t reference pop culture (such as “TARDIS”)
- Never use a password in more than once place
- Change your password regularly and use a different one for every website
- Don’t write passwords down, and don’t share them. Not with anybody. Ever!
The passwords you choose should increase Web Host Security by being obscure and not easy to work out. You’ll also help your security efforts if you give your root (Linux) or RDP (Windows) login its own unique password.
Linux security security needs a firewall
A firewall is a must have for web host security, because it’s your first line of defense against attackers, and you are spoiled for choice. NetFilter is built into the Linux kernel. Combined with iptables, you can use it to resist DDos attacks.
TCPWrapper is a host-based access control list (ACL) system that filters network access for different programs. It has host name verification, standardized logging and protection from spoofing. Firewalls like CSF and APF are also widely used, and they also come with plugins for popular panels like cPanel and Plesk.
Locking User Accounts After Unsuccessful Logins
For Linux security, the faillog command shows unsuccessful login attempts and can assign limits to how many times a user can get their login credentials wrong before the account is locked. faillog formats the contents of the failure log from the /var/log/faillog database/log file. To view unsuccessful login attempts, enter:
To open up an account locked in this way, run:
faillog -r -u userName
With Linux security in mind be aware that you can use the passwd command to lock and unlock accounts:
lock Linux account
passwd -l userName
unlock Linux account
passwd -u userName
Try disk partitions for better Web host security
If you partition your disks then you’ll be separating OS files from user files, tmp files and programs. Try disabling SUID/SGID access (nosuid) along with binaries (noexec) on the operating system partition
Avoid Using Telnet, FTP and Rlogin/Rsh Services
With the majority of network configurations, anyone on the same network with a packet sniffer can intercept FTP, telnet, or rsh commands, usernames, passwords, and transferred files. To avoid compromising Linux server security try using either OpenSSH, SFTP, or FTPS (FTP over SSL), which gives FTP the benefit of SSL or TLS encryption. To move outdated services like NIS or rsh enter this yum command:
# yum erase xinetd ypserv tftp-server telnet-server rsh-server
For Debian/Ubuntu Linux server security, give the apt-get command/apt command a try to get rid of non-secure services:
$ sudo apt-get --purge remove xinetd nis yp-tools tftpd atftpd tftpd-hpa telnetd rsh-server rsh-redone-server
Use an Intrusion Detection System
NIDS or Network intrusion detection systems keep watch for malevolent activity against Linux server security like DOS attacks, port scans, and intrusion attempts.
For greater Linux server security hardening it’s recommended that you use integrity checking software before you take a system into a production environment online. You should install AIDE software before connecting the system to a network if possible. AIDE is a host-based intrusion detection system (HIDS) which monitors and analyses a computing system’s internals. You would be wise to use rkhunter rootkit detection software as well.
Logs and Audits
You can’t manage what you don’t measure, so if you want to stop hackers then your system needs to log every single time that intruders try to find a way in. Syslog is set up to store data in the /var/log/ directory by default and it can also help you to identify the potential surreptitious routes inside that misconfigured software can present.
Secure Apache/PHP/NGINX server
Edit httpd.conf file and add:
Options all -Indexes
Header always unset X-Powered-By
Restart the httpd/apache2 server on Linux, run:
$ sudo systemctl restart apache2.service
$ sudo systemctl restart httpd.service
Activate CMS auto-updates
CMSs are quite complex, so hackers are always trying to exploit security loopholes with them. Joomla!, Drupal and WordPress, are all hugely popular platforms, so developers are constantly working on new security fixes. This means updates are important and should be applied straight away. The best way to ensure this happens is to activate auto-updates, so you won’t even have to think about it. Your host isn’t responsible for the content of your website. So it’s up to you to ensure you update it regularly. And it won’t hurt to back it up once in a while either.
Regular and thorough backups are probably your most important security measure. Backups can help you recover from a security disaster. Typical UNIX backup programs use dump and restore, and these are we recommend them. For maximum Linux security, you need to backup to external storage with encryption, which means something like a NAS server or cloud-based service.
Protect Email Directories and Files
These Linux security tips wouldn’t be complete without telling you that Linux has some great ways to protect data against unauthorized access. File permissions and MAC are great at stopping intruders from getting at your data, but all the Linux permissions in the world don’t count for anything if they can be circumvented—for instance, by transplanting a hard drive to another machine. In such a case you need to protect Linux files and partitions with these tools:
- For password-protected file encryption and decryption, use the gpg
- Both Linux and UNIX can add password protection to files using openssl and other tools.
- The majority of Linux distributions support full disk encryption. You should ensure that swap is encrypted too, and only allow bootloader editing via a password.
- Make sure root mail is forwarded to an account that you check.
System Accounting with auditd
Auditd is used for system audits. Its job is to write audit records to the disk. This daemon reads the rules in /etc/audit.rules at start-up. You have various options for amending the /etc/audit.rules file such as setting up the location for the audit file log. Auditd will help you gain insight into these common events:
- Occurrences at system startup and shutdown (reboot/halt).
- Date and time an event happened.
- The user who instigated the event (for example, perhaps they were attempting to access /path/to/topsecret.dat file).
- Type of event (edit, access, delete, write, update file, and commands).
- Whether the event succeeded or failed.
- Records events that Modify time and date.
- Discover who modified network settings.
- Record actions that change user or group information.
- Show who changed a file etc.
Kerberos is a third-party service offering authentication that aids Linux security hardening. It uses shared secret cryptography and assumes that packets moving on a non-secure network are readable and writable. Kerberos is based on symmetric-key cryptography and so needs a key distribution center. Kerberos lets you make remote login, remote copy, secure inter-system file copying, and other risky actions safer and it also gives you more control over them. Kerberos authentication prevents unauthorized users from spying on network traffic and grabbing passwords.
Hardening Security Of Your Linux Server Using Plesk
- Update Plesk on a regular basis
- Password should be set to at least Strong
- Filter any ports that aren’t being used with a firewall.
- Protect Plesk and a mail server with SSL/TLS certificates
- Enable a secure FTP connection
- Restrict which administrators can use Plesk
- Limit remote Access using XML API
- Set up Web Application Firewall (ModSecurity)
- WordPress Toolkit Security Check is the key to best practices for WordPress security
- Only use updated web apps, as older versions can contain security holes.
- Use VirusTotal Website Check. It can check websites using many anti-virus engines
- Use Google Authenticator/Authy extension for multi-factor authentication
- Grant access permissions to SSH access using a keyfile
- For SSH connections, avoid using a standard port
- Forbid SSH authentication for the root user
- Turn off Perl and Python if they are not needed for a website, and don’t ever use ‘mod_perl’ and ‘mod_python’ either.
- Try Immunify360. It’s an excellent all-round automated security solution for servers
- Set up ImunifyAV to protect websites from malware
- Use Fail2Ban for hack blocking protection
- Avoid using PHP handler for Apache as it isn’t safe
- Turn on automatic updates for system packages
- Use the KernelCare extension. It checks for and installs kernel updates, so you’ll never need to wonder if you’re using the most current version
- Set up the FTP passive port range on Linux
- Make sure that Apache doesn’t let the SSL 2.0/SSL 3.0 protocol run.
- You can find more advanced information about keeping Plesk for Linux secure here: Enhancing Security
Linux Server Security Summary
That’s a lot of tips, but you need to keep your linux server security updated in a world of thieves and vandals. These despicable beings are hard at work all the time, always looking to exploit any chink in a website’s armor. If you give them the slimmest opportunity to disrupt your business, they will happily take advantage of it. Since there’s such a huge army of them, you need to make sure that your castle has extremely strong defenses.
Let us know how many of these tips you have implemented, or if you have any questions in the comments below.