Security professional Michael Boelen writes about Linux security, system hardening, and related subjects. He worked as a consultant for multinational companies before he started CISOfy. Michael is involved with open source software and created several projects. Among them are Rootkit Hunter (rkhunter), a malware scanner for Linux and other platforms. He is also the creator and lead developer of Lynis, a tool that helps with hardening Linux systems. You can find more information about Michael on his website https://michaelboelen.com or via Twitter.

Hardening WordPress Security and Reduce Information Disclosure

WordPress and Reducing Information Leakage For years, WordPress is used as a platform for blogging. Last years, more and more companies have even built their website in WordPress. Unfortunately, this also means it is more often targetted by scripts, searching for their next victim. The primary reasons for a WordPress hack, are often disclosed information and outdated software components. This is applicable to the WordPress version itself and modules, like the plugins. In this article, we have a look at dealing […]

Read more

Granting temporary access to your servers (using signed SSH keys)

In need of support from a colleague or vendor, but don’t want to give them permanent access? SSH has an option to allow temporary access! Next time you need to provide temporary access for an hour or day, use this great option. Configuration We have two machines for this purpose. One is a system running Arch Linux, the client system. The other one is a server, running Ubuntu Linux. For temporary support, we have created a functional account support on the […]

Read more

Distributing SSH keys: using ssh-copy-id, manually or automated

Distribution of SSH keys When you want to allow public key authentication, you have to first create a SSH keypair. Next step is then the distribution of the public key to the other systems. Let’s have a look at a few options, including using the ssh-copy-id utility. Option 1: Manually In the past, you had to log in manually to the new system and do things yourself. Especially if you created your key with a tool like PuTTYgen on Windows. […]

Read more

Create random passwords with OpenSSL/LibreSSL

Random Passwords Generation As system administrators, we know we sometimes have to create passwords. It might be for ourselves, or when creating them for colleagues and customers. For an easy and quick way of generating random passwords, we can use the OpenSSL utility, part of OpenSSL and LibreSSL. This toolkit is often already installed on systems running Linux. OpenSSL has a randomize function. If we feed the output through the base64 function, the scrambled set of characters can be made more […]

Read more

Block IP addresses in Linux with iptables

Blocking IP addresses and subnets with ipset Most system administrators will already be familiar with iptables. It is around for quite a while and is enabled by default within the Linux kernel. We can use iptables to block one, multiple IP addresses, or even full networks. This may come in handy when you get repeating port scans or see failed login attempts in your log files. Time to get started and block some IP addresses! Check existing iptables configuration The first step is to […]

Read more

How to Disable “System program problem detected”

Quick Ubuntu Tips: System program problem detected   Sometimes programs crash, usually for a different variety of reasons. While it is good to do research and find the underlying cause, sometimes you simply want to disable any reporting. Clean up /var/crash First thing to do is check your /var/crash directory and see if there are any “crash” files. These are just normal text files and include details about a process. If you have a process crashing regularly, you most likely want to […]

Read more

Linux vulnerabilities: from detection to treatment

If you worked with a computer the last decade, you know the importance of keeping your software up-to-date. Those who don’t, are stacking up vulnerabilities, waiting for them to being exploited by others. Although Linux and most software are open source and can be reviewed, security flaws in software packages remain. While it isn’t easy to close every vulnerability on your system, we can at least create a stable process around it. This guide explains what is available, from vulnerability to […]

Read more

List network interfaces on Linux

The network configuration is a common place to start during system configuration, security audits, and troubleshooting. It can reveal useful information like MAC and IP addresses. This guide helps you to gather this information on Linux, including listing all available network interfaces and its details. Show network interfaces Linux Every Linux distribution is using its own way of configuring the network configuration details. Therefore, it is good to know which tools can be used to query these details in a generic […]

Read more

In-depth Linux Guide to Achieve PCI DSS Compliance and Certification

If you work for a company which accepts, processes, or stores credit card details, you might be familiar with the PCI Data Security Standard (DSS). The standard itself is very detailed. Still, it sometimes unclear on what specifically to implement and when. This guide will help with translating the PCI standard to technical security controls on Linux systems. This document has the goal to help you further secure your network and pass the PCI DSS audit. It is important to […]

Read more

Tiger is History, Long Live Modern Alternatives!

The History and Alternatives to the Tiger Security Tool Recently I saw some tweets showing up from an old friend: Tiger. Surprised to see it being promoted, as I know the tool for years, but never seen any new releases in the last years. Both are actually a shame. An outdated tool is usually of lower value. Promoting old tools might actually disappoint others and harm the initial trust in the software. History of Tiger In its day, the tool […]

Read more

Find Differences Between Two Daily Lynis Audits

Comparing Lynis Scan Results Lately I saw a great feature request for Lynis, to detect differences between two runs of Lynis. Wouldn’t it be great to run Lynis daily and then see if anything changes and act upon those differences? While our auditing tool doesn’t have such an option itself, it is very easy to implement something and fine-tune it to your needs. Report Lynis has two important files to which is logs data: /var/log/lynis.log /var/log/lynis-report.dat The first file /var/log/lynis.log has […]

Read more

Which Linux process is using a particular network port?

Most network related services have to open up a network socket, so they can start listening for incoming network requests. It is common to find the TCP or UDP being used as the main communication protocol. In this article, we will check what ports are used by which Linux process. Auditing processes and network services Find out what process is listening to a port Only one process can actively listen to a TCP or UDP port. We usually only discover […]

Read more

SOx compliance and Enron: The Smartest Guys in the Room

Enron: The Smartest Guys in the Room If you are involved with Linux security, you might already have come across SOx compliance. Usually from a sysadmins point of view, work doesn’t get easier due to these compliance requirements. Still there are some lessons we can learn, followed by a great documentary to watch about Enron. The Sabanes-Oxley Act, SOx for short, now applies to all companies who like to have their stock exchanged at the New York stock exchange (NYSE). The […]

Read more

Linux Security Principle: Containment of Failure

Containment of Failure Everyone who used Windows 95 or 98 in the past is familiar with the concept of failure. One crashing application was enough to bring the system to a halt. Fortunately, Linux systems have a strong foundation, including privilege separation and memory management. When things go wrong, the impact is reduced to a minimum. This is called containment. Linux Memory Management Memory is like your the storage capacity of your brain. Every bit should be stored properly, or otherwise […]

Read more

Missing Packages: Don’t Trust External Repositories!

Missing packages… If you are in the business of system administration, you know the big dilemma when it comes to installing software: missing packages. Yes, a lot of packages are available in the repositories of your Linux distribution, but not the one you need. Or when it is, it is horribly outdated. So you reach out to external resources, like community maintained repositories, right? With Lynis, we face this same issue. While most of the distributions have Lynis in the […]

Read more
14567815