Auditing Linux Operating System with Lynis

Auditing a Linux System is one of the most important aspect when it comes to security. After deploying a simple Centos 7 Linux machine on virtual box, I made an audit using Lynis. It is amazing how many tiny flaws can be seen right from the beginning of a fresh installation. Lynis Enterprise performs security scanning for Linux, macOS, and Unix systems. It helps you discover and solve issues quickly, so you can focus on your business and projects again.Cisofy.



The Lynis tool performs both security and compliance auditing. It has a free and paid version which comes very handy especially if you are on a business environment. The installation of the Lynis tool is pretty simple. You can install it through the Linux repository itself, download the tar file or clone it directly from Github.


Scanning Performed by Lynis

1. I downloaded the tar file with the following command:


2. Then, just untar the file and get into it

tar -xzf lynis-2.6.0.tar.gz && cd lynis

3. Once into the untar directory, launch the following command:

./lynis audit system --quick

As you can see from the output above, there are several suggestions at the end of the scan. In case the paid version of the application was used, more information and commands as how to remediate the situation would be given including support from Lynis. As regards to the free version, you can also debug by yourself several security aspects from the suggestions.
Suggestions, Compliance and Improvement.

1.The first two suggestions were about minimum and maximum password age.

Configure minimum password age in /etc/login.defs [AUTH-9286]

Configure maximum password age in /etc/login.defs [AUTH-9286]

To check the minimum and maximum password age, use the chage command :
chage -l

2. Use chage -m root to set the minimum password age and chage -M root to set maximum password age:

Also, you will have to set the parameter in the /etc/login.defs file

3. Delete accounts which are no longer used [AUTH-9288]

It is also suggested to delete accounts which are no longer in use. This suggestion was prompted as I created a user  “nitin” account during installation and did not use it yet. For the purpose of this blog, I deleted it using userdel -r nitin

4. Default umask in /etc/profile or /etc/profile.d/ could be more strict (e.g. 027) [AUTH-9328]

Default umask values are taken from the information provided in the /etc/login.defs file for RHEL (Red Hat) based distros. Debian and Ubuntu Linux based system use /etc/deluser.conf. To change default umask value to 027 which is actually 022 by default, you will need to modify the /etc/profile script as follows:

5. To decrease the impact of a full /home file system, place /home on a separated partition [FILE-6310]

  To decrease the impact of a full /tmp file system, place /tmp on a separated partition [FILE-6310]

  To decrease the impact of a full /var file system, place /var on a separated partition [FILE-6310]

In the article Move your /home to another partition, you will have detailed explanations to sort out this issue.

6. Disable drivers like USB storage when not used, to prevent unauthorized storage or data theft [STRG-1840]

   Disable drivers like firewire storage when not used, to prevent unauthorized storage or data theft [STRG-1846]

To disable USB and firewire storage drivers, add the following lines in /etc/modprobe.d/blacklist.conf then do a modprobe usb-storage && modprobe firewire-core

blacklist firewire-core
blacklist usb-storage

7. Split resolving between localhost and the hostname of the system [NAME-4406]

This issue is only about hostname and localhost in /etc/hosts which could confuse some applications installed on the machine. According to cisofy, for proper resolving, the entries of localhost and the local defined hostname, could be split. Using some middleware and some applications, resolving of the hostname to localhost, might confuse the software.

8. Install package ‘yum-utils’ for better consistency checking of the package database [PKGS-7384]

      Consider running ARP monitoring software (arpwatch,arpon) [NETW-3032]

The yum-utils and arpwatch are nice tools to perform more debugging and verification. Install it using the following commands:

yum install yum-utils arpwatch -y

9. You are advised to hide the mail_name (option: smtpd_banner) from your postfix configuration. Use postconf -e or change your file (/etc/postfix/ [MAIL-8818]

You just have to uncomment the following line and lauch a postconf -e. However, since this is a fresh install, and I’m not using postfix, it is better to stop the service.

 10.  Check iptables rules to see which rules are currently not used [FIRE-4513]

Since, I’m not on a production environment, it is very difficult to identify unused iptables rules right now. Once on the production environment, this situation is different. According to Cisofy, the best way is to “use iptables –list –numeric –verbose to display all rules. Check for rules which didn’t get a hit and repeat this process several times (e.g. in a few weeks). Finally remove any unneeded rules.”

 11. Consider hardening SSH configuration [SSH-7408]

  •     – Details  : AllowTcpForwarding (YES –> NO)
  •     – Details  : ClientAliveCountMax (3 –> 2)
  •     – Details  : Compression (YES –> (DELAYED|NO))
  •     – Details  : LogLevel (INFO –> VERBOSE)
  •     – Details  : MaxAuthTries (6 –> 2)
  •     – Details  : MaxSessions (10 –> 2)
  •     – Details  : PermitRootLogin (YES –> NO)
  •     – Details  : Port (22 –> )
  •     – Details  : TCPKeepAlive (YES –> NO)
  •     – Details  : UseDNS (YES –> NO)
  •     – Details  : X11Forwarding (YES –> NO)
  •     – Details  : AllowAgentForwarding (YES –> NO)

Again, hardening SSH is one of the most important to evade attacks especially from SSH bots. It all depends how your network infrastructure is configured and whether it is accessible from the internet or not. However, these details viewed are very informative.

12. Periodic system scan, malware and ransomware scanners are now a must. According to statistics, servers are being hacked constantly. Pervasive Monitoring is becoming a heavy cash deal for malicious softwares. 

The Lynis Command

Lynis documentation is pretty straight forward with a cheat sheet. The arguments are self explicit. Here are some hints.

1.Performs a system audit which is the most common audit.

lynis audit system

2. Provides command to do a remote scan.

lynis audit system remote <host>

3. Views the settings of default profile.

lynis show settings

4. Checks if you are using most recent version of Lynis

lynis update info

5. More information about a specific test-id

lynis show details <test-id>

6. To scan whole system

lynix --check-all Q

7. To see all available parameters of Lynis

lynis show options

At the end of any Lynis command, it will also prompt you where the logs have been stored for your future references. It is usually in /var/log/lynis.log. The systutorial on lynis is also a good start to grasp the command. All common systems based on Unix/Linux are supported. Examples include Linux, AIX, *BSD, HP-UX, macOS and Solaris. For package management, the following tools are supported:- dpkg/apt, pacman, pkg_info, RPM, YUM, zypper.

Happy New Year 2018 from TheTunnelix

My dear friends, readers and fellow bloggers, I would like to seize this opportunity as this is my last blog for the year 2017 to wish you and your family a Happy New Year 2018. There were lots of events in the month of November – December 2017. For today, I’m having a drink with family and friends. Oh yeah, Tomorrow, will be a super party 🙂

Those who missed events recently, in the month of November was about the Infotech 2017 where was present on our special stand busy evangelising OpenSource products. Our accomplishments were also displayed. Logan, from the team also made an amazing speech at the video conference room.

The team also had an end of year get together and lunch in a restaurant at Rose-Hill.

I’m happy to be able to complete my VMware Certified Administrator and VMware Certified Administrator Professional exams. I’m looking forward for more certifications next year. This year has marked the history of Mauritius where lot’s of Open Source contributions were carried out from Mauritians, mainly by Right now, we have several stuffs in our pipeline. Surprise soon 🙂

IT and Internet Users of Dodoland by

Since the split of the Linux community in Mauritius, was born. A new vision and objectives were the foundation of the core group. Our aim is to reach more people who will code in softwares that are used worldwide. The family kept growing. Today, we have brought more members in the community and right now, there is a boom in this group. Additionally, people from various part of the world wants to be part of the group, as seen on our Facebook group. has been hosting live video streams on YouTube to bring together more people willing to learn and share in the community.

Just chill. Let me get back to the title of this blog – IT and Internet Users of Dodoland! On Saturday, the 18th of November 2017, I was at the University of Mauritius together with Logan. We were joined by Yash Paupiah and Jagveer Loky. A presentation was carried out on “Introduction to Github” and the launch of the Mailing List called the “IT and Internet Users of Dodoland”. During the presentation, Logan brushed over the importance of having a Github account as well as sharing one’s code on it.

Presentation by Logan at the University of Mauritius

An example is to publish one’s assignment by a student. This acts as a catalyst for the academic development of the student. Today, companies will usually search the Github account of people, including Mauritians before recruiting them. Students were encouraged to create their Github accounts and even a blog. Then, we discussed about the achievement in the IETF 100 Hackathon. Logan took an example of Yash Paupiah’s who did some scripting two years back and now sending patch in the open source community. For example, the patches about TLS 1.3 during the IETF 100 Hackathon. At the end of the session, we announced the creation of the Mailing List “IT and Internet Users of Dodoland”. Jagveer Loky from the community was chosen to be the moderator of the mailing list. He will ensure the proper and smooth running of the mailing list.

At the University of Mauritius

At the end of the presentation, we had conversations with the students who were interested in topics such as OpenSSH, MVC, Java Programming, and MongoDB. Notes were taken to focus on these topics in the days to come. Then, we headed to Flying Dodo Bagatelle to celebrate the launch of the new mailing list by the team.

Celebrating with beer and pizza at Flying Dodo Bagatelle

We also had a video stream, where we were joined by other people from the community who came forward asking questions about the IETF 100 Hackathon and on several aspects of TLS1.3. Jagveer shoot a question as to whether people knew about the IETF in Mauritius. Of course, many knows about the IETF, but at what level is the contribution? As a technical guy, merely watching what’s going on at an IETF Hackathon does not make sense but instead contributions should be carried out in terms of codes to make the OpenSource community more rigid. 

Video Stream from Yesternight

At, we kept on innovating to transmit the messages through the internet as well as on the ground. Weeks back, we were also at the University of Mauritius where we met Yashtir Gopee who is a passionate of robotics and Artificial Intelligence. He also joined the community and is willing to join the “IT and Internet Users of Dodoland” Mailing List.

Yashtir and Logan

Indeed, we have come a long way since the creation of In such short time, we have been able to meet our objectives and we are continuing towards innovations and quality work in the group. I am looking forward that people make good use of the Mailing List and bring forward their issues as well as their contributions. Click to join the Mailing list.

IETF 100 hackathon on TLS 1.3 by

Some days back, The Register mentioned about preparing for IETF100 hackathon. Hooray! Yeah we did it and the hard work finally paid off thanks to the core team and the whole of team. After registering on the IETF – Internet Engineering Task Force website, the team set itself on the TLS1.3 API source code. We were all focused on the OpenSSL codes.

Once in our office, we set up the network and our equipment. Check out logan’s blog to have an idea how things went on. That’s true we struggled in the beginning, but finally we could see the light at the end of the tunnel. Patience and patience is all what you need and a calm mind to study how things are in the code. The testing was then carried out to confirm the beauty of the TLS 1.3 codes in our chosen projects. You can also view the TLS tutorial which explains the objectives of TLS1.3. For example: Mitigation of pervasive monitoring.

Here are some hints about the security from TLS1.3

  • RSA key was removed.
  • Stream ciphers was reviewed.
  • Removal of compressed data mechanism which was able to influence which data can be sent.
  • Renegotiation was removed.
  • SHA1 and Block ciphers were removed.
  • Use of modern cryptography like A-EAD.
  • Use of modern key such as PSK.

For more details see this blog from OpenSSL. We were also working together with the TLS team in Singapore which was lead by Nick Sullivan, champion at the IETF TLS hackathon.

After the IETF Hackathon, it was announced publicly about the good job done by the team on the IETF channel.

The team at the beach 🙂

More links :

PS: Any more links related to IETF Hackathon TLS 1.3 let me know, I will add it here!

Feel free to join the community group on Facebook and follow us on our Twitter account.

Securing MySQL traffic with Stunnel in a jail environment on CentOS

Stunnel is a program by Michal Trojnara that allows you to encrypt arbitrary TCP connections inside SSL. Stunnel can also allow you to secure non-SSL aware daemons and protocols (like POP, IMAP, LDAP, etc) by having Stunnel provide the encryption, requiring no changes to the daemon’s code. It is a proxy designed to add TLS encryption functionality to existing clients and servers without any changes in the programs’ code. Its architecture is optimized for security, portability, and scalability (including load-balancing), making it suitable for large deployments. –

The concept that lies behind Stunnel is about the encryption methodology that is used when the client is sending a message to a server using a secure tunnel. In this article, we will focus on using MySQL alongside Stunnel. MariaDB Client will access the MariaDB server database using the Stunnel for more security and robustness.

Photo Credits:
Photo Credits:

I will demonstrate the installation and configuration using the CentOS distribution which is on my Virtual Box lab environment. I created two CentOS 7 virtual machines with hostname as stunnelserver and stunnelclient. We will tunnel the MySQL traffic via Stunnel. You can apply the same concept for SSH, Telnet, POP, IMAP or any TCP connection.

The two machines created are as follows:

  1. stunnelserver : – Used as the Server
  2. stunnelclient : – Used as the Client

Basic package installation and configuration on both servers

1. Install the Stunnel and OpenSSL package on both the client and the server.

yum install stunnel openssl -y

2. As we will be using Stunnel over MariaDB, you can use the MariaDB repository tools to get the links to download the repository. Make sure you have the MariaDB-client package installed on the stunnelclient which will be used as client to connect to the server. Also, install both packages on the stunnelserver. The commands to install the MariaDB packages are as follows:

sudo yum install MariaDB-server MariaDB-client

3. For more information about installations of MariaDB, Galera etc, refer to these links:

MariaDB Galera Clustering

MariaDB Master/Master installation

MariaDB Master/Slave installation

Configuration to be carried out on the stunnelserver (


4. Once you have all the packages installed, it’s time to create your privatekey.pem. Then, use the private key to create the certificate.pem. Whilst creating the certificate.pem, it will prompt you to enter some details. Feel free to fill it.

openssl genrsa -out privatekey.pem 2048

openssl req -new -x509 -days 365 -key privatekey.pem -out certificate.pem

5. Now comes the most interesting part to configure the stunnel.conf file by tunnelling it to the MySQL port on the stunnelserver. I observed that the package by default does not come with a stunnel.conf or even a Init script after installing it from the repository. So, you can create your own Init script. Here is my /etc/stunnel/stunnel.conf on the server:

chroot = /var/run/stunnel
setuid = stunnel
setguid = stunnel
pid /
debug = 7
output = /stunnel.log
sslVersion = TLSv1
key = /etc/stunnel/privatekey.pem
cert = /etc/stunnel/certificate.pem
accept = 44323
connect =

6. Position your privatekey.pem and certificate.pem at /etc/stunnel directory. Make sure you have the right permission (400) on the privatekey.pem.

7. Based upon the configuration in part 5, we will now create the /var/run/stunnel directory and assign it with user and group of stunnel:

useradd -G stunnel stunnel && mkdir /var/run/stunnel && chown stunnel:stunnel /var/run/stunnel

8.  The port 44323 is a non reserved port which I chose to tunnel the traffic from the client.

9. As we do not have the Init script by default in the package, start the service as follows:

stunnel /etc/stunnel/stunnel.conf

10. A netstat or ss command on the server will show the Stunnel listening on port 44323.

Configuration to be carried out on the stunnelclient (

11. Here is the stunnel.conf file on the stunnel client :

verify = 2
chroot = /var/run/stunnel
setuid = stunnel
setguid = stunnel
pid = /
CAfile = /etc/stunnel/certificate.pem
client = yes
sslVersion = TLSv1
renegotiation = no
accept = 24
connect =

12. Import the certificate.pem in the /etc/stunnel/ directory.

scp <user>@<ipofstunnelserver>:/etc/stunnel/certificate.pem

13. Based upon the configuration in part 11, we will now create the /var/run/stunnel directory and assign it with user and group of stunnel:

useradd -G stunnel stunnel && mkdir /var/run/stunnel && chown stunnel:stunnel /var/run/stunnel

14. You can now start the service on the client as follows:

stunnel /etc/stunnel/stunnel.conf

15. A netstat on the client will show the Stunnel listening on port 24.

16. You can now connect on the MySQL database from your client to your server through the tunnel. Example:

mysql -h -u <Name of Database> -p -P 24


  • When starting Stunnel, the log and the pid file will be created automatically inside the jail environment that is /var/run/stunnel.
  • You can also change the debug log level. Level is a one of the syslog level names or numbers emerged (0), alert (1), crit (2), err (3), warning (4), notice (5), info (6), or debug (7). All logs for the specified level and all levels numerically less than it will be shown. Use debug = debug or debug = 7 for greatest debugging output. The default is notice (5).
  • If you compile from source, you will have a free log rotate and Init scripts. Probably on CentOS, it’s not packaged with the script!
  • You can also verify if SSLv2 and SSLv3 have been disabled using openssl s_client -connect -ssl3 and try with -tls1 to compare.
  • For the purpose of testing, you might need to check your firewall rules and SELINUX parameters.
  • You don’t need MariaDB-Server package on the client.
  • Stunnel is running on a Jail environment. The logs and the PID described in part 5 and 11 will be found in /var/run/stunnel.
  • You can invoke stunnel from inetd. Inetd is the Unix ‘super server’ that allows you to launch a program (for example the telnet daemon) whenever a connection is established to a specified port. See the “Stunnel how’s to” for more information. The Stunnel manual can also be viewed here.