Linux, often referred to as "just the kernel," forms the foundation for a wide range of operating systems that power much of today’s digital infrastructure.
From web servers to supercomputers, and even the "smart" devices in homes, Linux is everywhere. The popularity of Linux is not surprising, as it provides flexibility, scalability, and open-source power to its users.
While "Linux" technically refers to the kernel, in real-world discussions, the term often describes the full operating system, which is better defined by its "distribution" (distro). Distributions vary widely and are frequently created or customized by users, making incident response (IR) on Linux environments a unique and challenging endeavor.
Why Linux Matters in Incident Response
Linux has been widely adopted in corporate environments, particularly for public-facing servers, critical infrastructure, and cloud deployments. By 2030, it is projected that an overwhelming majority of public web servers will continue to rely on Linux. Currently, Linux dominates the server landscape, with 96.3% of the top one million web servers using some version of it . Even in largely Windows-based organizations, the Linux kernel powers essential infrastructure like firewalls, routers, and many cloud services.
Understanding Linux is crucial for incident responders as more enterprises embrace this operating system, making it essential to gather, analyze, and investigate data across multiple platforms, including Linux.
Understanding Linux Distributions
When we talk about Linux in an IR context, we’re often referring to specific distributions. The term "Linux distro" describes the various versions of the Linux operating system, each built around the Linux kernel but offering different sets of tools and configurations.
Linux distros tend to fall into three major categories:
Debian-based: These include Ubuntu, Mint, Kali, Parrot, and others. Debian-based systems are commonly seen in enterprise and personal computing environments.
Red Hat-based: Including RHEL (Red Hat Enterprise Linux), CentOS, Fedora, and Oracle Linux. These distros dominate enterprise environments, with 32% of servers running RHEL or a derivative.
Others: Distros like Gentoo, Arch, OpenSUSE, and Slackware are less common in enterprise settings but still exist, especially in niche use cases.
With such diversity in Linux environments, incident responders must be aware of different configurations, logging systems, and potential variances in how Linux systems behave.
For keeping track of changes and trends in distros, DistroWatch is a great resource:
Key Challenges in Incident Response on Linux
1. System Complexity and Configuration
One of the main challenges of Linux is its configurability. Unlike Windows, where settings are more standardized, Linux can be customized to the point where two servers running the same distro may behave very differently.
For example, log files can be stored in different locations, user interfaces might vary, and various security or monitoring tools may be installed. This flexibility makes it difficult to develop a “one-size-fits-all” approach to IR on Linux.
2. Inexperienced Administrators
Many companies struggle to hire and retain experienced Linux administrators, leading to common problems such as insecure configurations and poorly maintained systems. Without adequate expertise, it’s common to see servers running default settings with little hardening. This can result in minimal logging, excessive privileges, and other vulnerabilities.
3. Minimal Tooling
While Linux is incredibly powerful, security tools and incident response capabilities on Linux lag behind what is available for Windows environments. As a result, responders may find themselves lacking the familiar tools they would use on a Windows system. Performance issues on Linux-based security tools often force incident responders to improvise, using a mix of built-in Linux utilities and third-party open-source tools.
One way to address this issue is by using cross-platform EDR tools like Velociraptor, which provide consistency across environments and can help streamline investigations on Linux systems.
4. Command Line Dominance
Linux's reliance on the command line is both a strength and a challenge. While GUIs exist, many tasks—especially for incident response—are done at the command line. Responders need to be comfortable working with shell commands to gather evidence, analyze data, and conduct investigations. This requires familiarity with Linux utilities like grep, awk, tcpdump, and others.
5. Credential Issues
Linux systems are often configured with standalone credentials, meaning they don’t always integrate seamlessly with a company’s domain or credential management system. For incident responders, this presents a problem when gaining access to a system as a privileged user. In cases where domain credentials aren’t available, IR teams should establish privileged IR accounts that use key-based or multi-factor authentication, ensuring that any usage is logged and monitored.
Attacking Linux: Common Threats
There’s a widespread myth that Linux systems are more secure than other operating systems or that they aren’t attacked as frequently. In reality, attackers target Linux systems just as much as Windows, and the nature of Linux creates unique attack vectors.
1. Insecure Applications
Regardless of how well the operating system is hardened, a poorly configured or vulnerable application can open the door for attackers. One common threat on Linux systems is web shells, which attackers use to establish backdoors or maintain persistence after initial compromise.
2. Pre-Installed Languages
Many Linux systems come pre-installed with powerful scripting languages like Python, Ruby, and Perl. While these languages provide flexibility for administrators, they also provide opportunities for attackers to leverage "living off the land" techniques. This means attackers can exploit built-in tools and languages to carry out attacks without needing to upload external malware.
3. System Tools
Linux comes with many powerful utilities, like Netcat and SSH, that can be misused by attackers during post-exploitation activities. These tools, while helpful to administrators, are often repurposed by attackers to move laterally, exfiltrate data, or maintain persistence on compromised systems
Conclusion
Linux is everywhere, from cloud platforms to enterprise firewalls, and incident responders must be prepared to investigate and mitigate incidents on these systems. While the challenges of Linux IR are significant—ranging from custom configurations to limited tooling—preparation, training, and the right tools can help defenders overcome these hurdles.
Akash Patel.
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