Welcome!

Linux Authors: Carmen Gonzalez, Liz McMillan, Jim Kaskade, Aater Suleman, Mike Kavis

Related Topics: Linux, Open Source

Linux: Blog Feed Post

Twenty-Five Linux Server Hardening Tips

A compilation of various settings and techniques you can employ

linux securityWhen it comes to having a Linux server hosted in a data center or it is not behind any kind of Firewall or NAT device there are a number of security requirements that need to be addressed. Linux servers generally come with no protection configured by default and depending on the hosting company or distro can come preconfigured with many services installed that are not required, including Web Servers, FTP Servers, Mail Servers and SSH Remote Access.

The following is a compilation of various settings and techniques you can employ to harden the security of your vulnerable Linux systems. While I have tried to put them in order of the most important features first I would recommend all of these options be used on your critical production servers.

TIP #1 – Strong Passwords
Always create long passwords that contain upper and lower case letters, numbers and non alpha-numeric characters. Enforce password ageing so users need to change their passwords regularly. Lock user accounts after a certain number of failed login attempts.

TIP #2 – Use Public/Private Keys
Make use of Public/Private SSH keys for login of remote users instead of passwords, this provides the benefit of turning off password authentication in SSH so that your server can’t be Brute-Force cracked. However this does introduce a new problem whereby a malicious person could compromise a user’s computer or steal their laptop and then have access to the server. This can be overcome by using a password on the client certificate which must be entered before connecting, a kind of two factor authentication.

TIP #3 – Disable Root Login
Disable the Root user from being able to login either via the console or remote SSH connections. Instead have users use Sudo to run programs that require root privileges, or use sudo su to change to the Root user once logged in. This provides an audit path to show which user installed a piece of software or ran a program.

TIP #4 – Use Encrypted Traffic
Always use the encrypted equivalent protocol when transferring critical and sensitive data such as passwords and confidential material. Remove RSH and always use SSH for remote access. Instead of using FTP for file transfer, consider using SFTP or FTP/S (FTP over SSL) or RSYNC. Instead of having remote access open to the internet i.e. SSH or VNC setup an OpenVPN SSL VPN Server to connect to first.

TIP #6 – Use Centralized Password Server
Consider implementing either a LDAP or Kerebos server to perform password authentication. This allows for a central database to maintain user’s passwords between multiple servers for easy management. This prevents user account and password data from becoming inconsistent and out of date, and prevents user accounts that should have been deleted on all servers being left behind on one server.

TIP #7 – Use IPTABLES Firewall/TCP Wrapper
Implementing a secure IPTABLES firewall will limit your exposure to network threats such as DOS and Port Scanning attacks. You can lock down any ports that don’t require access from external networks. For instance you can use the following command to only allow SSH access to the server from the local network.


# iptables –A INPUT –s 192.168.0.0/24 –p tcp –dport 22 –j ACCEPT


You can install a TCP Wrapper named libwrap which will give information like who connected, when and from where and even which services they connected to. It can also be used for locking down access to ports and services for certain hosts or IP’s.

TIP #8 – Use Intrusion Detection Systems
Consider installing both a Network IDS (NIDS) and a Host Based IDS (HIDS). NIDS’s are used to protect against malicious threats such as DOS and Port Scan Attacks. HIDS’s such as AIDE are used to monitor file system changes such as an intruder replacing core system files like ls or ps with malicious ones that hide their Trojan from file or process lists. It will produce a report that tells you what files have been modified so you can repair or replace them.

TIP #9 – Users Assigned Least Privileges
Disable Shell access to users that don’t need it (ftp, mail users etc) by changing to /bin/noshell in the /etc/passwd file. Setup a group for standard users and remove permissions to tools that can be used to download malicious software like wget, lynx, ftp etc. Consider chrooting users to their home directories to stop them from modifying critical system files.

TIP #10 – Minimize Software
Only install software that is actually needed, some systems come preconfigured with many software packages that you may never need or use. When installing always choose the Minimal Installation or Manual Installation option if they exist. Then simply install the software that you actually need.

TIP #11 – Keep Software Updated
Always try to keep your software packages up to date, such as ensuring the latest version of Apache, MySQL and PHP on a standard LAMP setup will protect you against any vulnerabilities that have been discovered in previous versions.

TIP #12 – Disable Unwanted Services
Your servers will most likely have many background services (Daemons) running which are not required and some may be configured to run on start-up. The following command (Red Hat, Cent OS only) can be used to show all services that will start on boot.


# chkconfig --list | grep : on


Or just use the following command to view services which are turned on only for Run Level 3.


# chkconfig --list | grep 3:on


You would then use a command like this to remove the service from start-up.


# chkconfig --del ‘service-name’


TIP #13 – Remove X Windows
Consider completely removing X Windows from the system and just using the command line for management. There isn’t anything that you can do in the GUI that you can’t do using the command line and removing it will not only enhance security but also performance because no system resources are wasted displaying the GUI.

TIP #14 – Secure Linux Kernel
You can secure your Linux Kernel by modifying the /etc/sysctl.conf file, this file is read by the Kernel at boot time and can be edited with the following settings to add extra security.


# Turn on execshield
kernel.exec-shield = 1
kernel.randomize_va_space = 1
# Don't reply to broadcasts. Prevents joining a smurf attack
net.ipv4.icmp_echo_ignore_broadcasts = 1
# Enable protection for bad icmp error messages
net.ipv4.icmp_ignore_bogus_error_responses = 1
# Enable syncookies for SYN flood attack protection
net.ipv4.tcp_syncookies = 1
# Enable IP spoofing protection
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
# Log spoofed, source routed, and redirect packets
net.ipv4.conf.all.log_martians = 1
net.ipv4.conf.default.log_martians = 1
# Don't allow source routed packets
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
# Don't allow outsiders to alter the routing tables
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
# Don't pass traffic between networks or act as a router
net.ipv4.ip_forward = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0


TIP #15 – Install Linux Kernel Patches
You should have a written security policy for handling Linux Kernel Patches, which should include which Linux security notices have been received, which updates have been tested to ensure problems don’t arise and which patches have been installed on the system. Always ensure Production servers are updated regularly to avoid any potential known vulnerability from being exploited on your system.

TIP #16 – Separate Partitions
You should create separate partitions for user modifiable directories and block write and execute access to unneeded partitions. You should consider placing the following file systems on different partitions.
/usr
/home
/var and /var/tmp
/tmp

Then you can edit the /etc/fstab file to prevent execution of binary files, disable block devices on the partition and prevent the SUID/SGID from being set on files. Here is a common fstab file entry to limit user access to the ftpdata directory.


/dev/sda5  /ftpdata  ext3    defaults,noexec,nodev,nosuid 1 2


TIP #17 – Use Linux Security Extensions
Make use of software like SELinux, AppArmor or GRSecurity to provide additional hardening to your Linux Kernel. These products provide additional policies to restrict processes and services based on Access Control Lists.

TIP #18 – Separate Servers for Services
Consider setting up different physical or virtual servers for different roles, i.e. separate your Mail server and your Webserver, or your Database server and your Application server. This ensures that if one particular service is compromised it is contained to just one server.

TIP #19 – Physical Server Security
You can secure your server as much as possible from remote attacks, but if you don’t do anything to protect the physical hardware it is pointless. If someone has access to your physical server they can remove your hard drive and read your confidential data or boot from a CD and access your data. Consider creating a BIOS password and disabling booting from CD or USB. Also you should password protect your boot loader (GRUB, LILO, etc) to prevent users from accessing Single User Mode or Recovery Environments where passwords are not required.

TIP #20 – Setup NTP
Having an accurate system clock is important for reviewing log files and determining when an event occurred. Often system clocks can become out of sync or be reset to an older date and this can cause havoc with tracking of errors. Consider creating a Cron job rather than running ntpd (See Tip #12) to update the time daily or hourly with a common source for all servers.

TIP #21 – Monitor All Logs
Setup logging and auditing software to track errors and changes to your servers, such as Auditd and Logwatch/Logcheck. Consider configuring a remote logging server that is updated regularly to protect against an intruder compromising your log files without your knowledge.

TIP #22 – Disable IPv6
IPv6 is very rarely needed at this stage as most traffic only utilizes IPv4 and having IPV6 enabled is just another network you need to monitor and protect. Disabling IPv6 is the easiest option but if for some reason you do require it then you should configure an IPv6 Firewall.

TIP #23 – Remove SUID and SGID from Files
After you have setup and configured your system and software you should run the following commands to search for all file and folders with either the SUID, SGID bit set or world writeable folders.
To find all SUID files:


# find / -xdev -type f -perm +u=s –print


To find all SGID files:


# find / -xdev -type f -perm +g=s -print


To find all World Writeable Dirs:


# find / -xdev -perm +o=w ! \( -type d -perm +o=t \) ! -type l -print


You should then inspect each file and folder to determine if they have the correct settings and if not use the chmod command to make changes to them.

TIP #24 – Encrypt Confidential Data
Your data is usually stored on a hard drive in an unencrypted format so any user that has access to the server can remove the hard drive and install it in another system and read all your data. You should consider configuring Linux disk or folder encryption on either your home directories or your sensitive folders (i.e. Database Files, Emails, etc). While you could encrypt your entire drive this is a lot of work and may not be worth the hassle.

TIP #25 – Harden Your Software
It is great to have a highly secure Linux server but your system is only secure as the software you run on it. You should always install the latest versions of software and ensure they stay up to date. Also most programs have ways to make them more secure by editing their configuration files and disabling unnecessary parts of the software. The following is an example for hardening your OpenSSH Server settings, simply add the following  to your OpenSSH config file.


# Use only SSH Protocol Ver 2
Protocol 2
# Only allow the following users SSH Access
AllowUsers User1 User2 etc
# Deny access to the following users
DenyUsers admin etc
# Set the timeout period for idle sessions (in seconds)
ClientAliveInterval 300
ClientAliveCountMax 0
# Disable .rhosts files
IgnoreRhosts yes
# Disable Host-Based Authentication
HostbasedAuthentication no
# Remove ability to login as Root
PermitRootLogin no
# Change the default SSH Port (Not essential but can help uncomment if you want)
#Port 22
#ListenAddress 192.168.1.1
# Consider CHRooting users to their own directories.
# Subsystem sftp internal-sftp
#Match group sftponly
#         ChrootDirectory /home/%u
#         X11Forwarding no
#         AllowTcpForwarding no
#         ForceCommand internal-sftp
# Disable empty passwords from login
PermitEmptyPasswords no
# Set your required Log Level (Either INFO or DEBUG)
LogLevel INFO
#  Turn on privilege separation
UsePrivilegeSeparation yes
# Prevent the use of insecure home directory and key file permissions
StrictModes yes
# Turn on  reverse name checking
VerifyReverseMapping yes
# Do you need port forwarding?
AllowTcpForwarding no
X11Forwarding no
#  Specifies whether password authentication is allowed.  The default is yes.
PasswordAuthentication no


Monitis is an all-in-one hosted monitoring platform for small and medium-sized businesses. 70,000+ IT pros use Monitis products to monitor health and performance of over 300,000 sites.

Read the original blog entry...

More Stories By Hovhannes Avoyan

Hovhannes Avoyan is the CEO of Monitis, Inc., a provider of on-demand systems management and monitoring software to 50,000 users spanning small businesses and Fortune 500 companies.

Prior to Monitis, he served as General Manager and Director of Development at prominent web portal Lycos Europe, where he grew the Lycos Armenia group from 30 people to over 200, making it the company's largest development center. Prior to Lycos, Avoyan was VP of Technology at Brience, Inc. (based in San Francisco and acquired by Syniverse), which delivered mobile internet content solutions to companies like Cisco, Ingram Micro, Washington Mutual, Wyndham Hotels , T-Mobile , and CNN. Prior to that, he served as the founder and CEO of CEDIT ltd., which was acquired by Brience. A 24 year veteran of the software industry, he also runs Sourcio cjsc, an IT consulting company and startup incubator specializing in web 2.0 products and open-source technologies.

Hovhannes is a senior lecturer at the American Univeristy of Armenia and has been a visiting lecturer at San Francisco State University. He is a graduate of Bertelsmann University.

@ThingsExpo Stories
SYS-CON Events announced today that Harbinger Systems will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Harbinger Systems is a global company providing software technology services. Since 1990, Harbinger has developed a strong customer base worldwide. Its customers include software product companies ranging from hi-tech start-ups in Silicon Valley to leading product companies in the US and large in-house IT organizations.
SYS-CON Events announces a new pavilion on the Cloud Expo floor where WebRTC converges with the Internet of Things. Pavilion will showcase WebRTC and the Internet of Things. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices--computers, smartphones, tablets, and sensors – connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades.
The only place to be June 9-11 is Cloud Expo & @ThingsExpo 2015 East at the Javits Center in New York City. Join us there as delegates from all over the world come to listen to and engage with speakers & sponsors from the leading Cloud Computing, IoT & Big Data companies. Cloud Expo & @ThingsExpo are the leading events covering the booming market of Cloud Computing, IoT & Big Data for the enterprise. Speakers from all over the world will be hand-picked for their ability to explore the economic strategies that utility/cloud computing provides. Whether public, private, or in a hybrid form, clo...
SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual Controller™ Technology (SVCT) to eliminate the I/O blender effect and accelerate applications Gridsto...
SYS-CON Events announced today that Red Hat, the world's leading provider of open source solutions, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Red Hat is the world's leading provider of open source software solutions, using a community-powered approach to reliable and high-performing cloud, Linux, middleware, storage and virtualization technologies. Red Hat also offers award-winning support, training, and consulting services. As the connective hub in a global network of enterprises, partners, a...
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at Internet of @ThingsExpo, Andrew Bolwell, Director of Innovation for HP’s Printing and Personal Systems Group, will discuss how key attributes of mobile technology – touch input, senso...
The Internet of Things (IoT) is making everything it touches smarter – smart devices, smart cars and smart cities. And lucky us, we’re just beginning to reap the benefits as we work toward a networked society. However, this technology-driven innovation is impacting more than just individuals. The IoT has an environmental impact as well, which brings us to the theme of this month’s #IoTuesday Twitter chat. The ability to remove inefficiencies through connected objects is driving change throughout every sector, including waste management. BigBelly Solar, located just outside of Boston, is trans...
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, will examine three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics...
Internet of @ThingsExpo Silicon Valley announced on Thursday its first 12 all-star speakers and sessions for its upcoming event, which will take place November 4-6, 2014, at the Santa Clara Convention Center in California. @ThingsExpo, the first and largest IoT event in the world, debuted at the Javits Center in New York City in June 10-12, 2014 with over 6,000 delegates attending the conference. Among the first 12 announced world class speakers, IBM will present two highly popular IoT sessions, which will take place November 4-6, 2014 at the Santa Clara Convention Center in Santa Clara, Calif...
The Internet of Things (IoT) promises to evolve the way the world does business; however, understanding how to apply it to your company can be a mystery. Most people struggle with understanding the potential business uses or tend to get caught up in the technology, resulting in solutions that fail to meet even minimum business goals. In his session at Internet of @ThingsExpo, Jesse Shiah, CEO / President / Co-Founder of AgilePoint Inc., will show what is needed to leverage the IoT to transform your business. He will discuss opportunities and challenges ahead for the IoT from a market and tec...
SYS-CON Events announced today that TeleStax, the main sponsor of Mobicents, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. TeleStax provides Open Source Communications software and services that facilitate the shift from legacy SS7 based IN networks to IP based LTE and IMS networks hosted on private (on-premise), hybrid or public clouds. TeleStax products include Restcomm, JSLEE, SMSC Gateway, USSD Gateway, SS7 Resource Adaptors, SIP Servlets, Rich Multimedia Services, Presence Services/RCS, Diame...
From a software development perspective IoT is about programming "things," about connecting them with each other or integrating them with existing applications. In his session at @ThingsExpo, Yakov Fain, co-founder of Farata Systems and SuranceBay, will show you how small IoT-enabled devices from multiple manufacturers can be integrated into the workflow of an enterprise application. This is a practical demo of building a framework and components in HTML/Java/Mobile technologies to serve as a platform that can integrate new devices as they become available on the market.
SYS-CON Events announced today that O'Reilly Media has been named “Media Sponsor” of SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. O'Reilly Media spreads the knowledge of innovators through its books, online services, magazines, and conferences. Since 1978, O'Reilly Media has been a chronicler and catalyst of cutting-edge development, homing in on the technology trends that really matter and spurring their adoption by amplifying "faint signals" from the alpha geeks who are creating the future. An...
The Transparent Cloud-computing Consortium (abbreviation: T-Cloud Consortium) will conduct research activities into changes in the computing model as a result of collaboration between "device" and "cloud" and the creation of new value and markets through organic data processing High speed and high quality networks, and dramatic improvements in computer processing capabilities, have greatly changed the nature of applications and made the storing and processing of data on the network commonplace.
SYS-CON Events announced today that Aria Systems, the recurring revenue expert, has been named "Bronze Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Aria Systems helps leading businesses connect their customers with the products and services they love. Industry leaders like Pitney Bowes, Experian, AAA NCNU, VMware, HootSuite and many others choose Aria to power their recurring revenue business and deliver exceptional experiences to their customers.
The Internet of Things (IoT) is going to require a new way of thinking and of developing software for speed, security and innovation. This requires IT leaders to balance business as usual while anticipating for the next market and technology trends. Cloud provides the right IT asset portfolio to help today’s IT leaders manage the old and prepare for the new. Today the cloud conversation is evolving from private and public to hybrid. This session will provide use cases and insights to reinforce the value of the network in helping organizations to maximize their company’s cloud experience.
As a disruptive technology, Web Real-Time Communication (WebRTC), which is an emerging standard of web communications, is redefining how brands and consumers communicate in real time. The on-going narrative around WebRTC has largely been around incorporating video, audio and chat functions to apps. In his session at Internet of @ThingsExpo, Alex Gouaillard, Founder and CTO of Temasys Communications, will look at a fourth element – data channels – and talk about its potential to move WebRTC beyond browsers and into the Internet of Things.
SYS-CON Events announced today that Gigaom Research has been named "Media Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Ashar Baig, Research Director, Cloud, at Gigaom Research, will also lead a Power Panel on the topic "Choosing the Right Cloud Option." Gigaom Research provides timely, in-depth analysis of emerging technologies for individual and corporate subscribers. Gigaom Research's network of 200+ independent analysts provides new content daily that bridges the gap between break...
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
The Industrial Internet revolution is now underway, enabled by connected machines and billions of devices that communicate and collaborate. The massive amounts of Big Data requiring real-time analysis is flooding legacy IT systems and giving way to cloud environments that can handle the unpredictable workloads. Yet many barriers remain until we can fully realize the opportunities and benefits from the convergence of machines and devices with Big Data and the cloud, including interoperability, data security and privacy.