Hardening

When configuring a new device, achieving an acceptable Lynis hardening score is a challenge most practitioners are familiar with.

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Hardening a Linux client system to an acceptable degree is a time-consuming process, one that demands familiarity with a broad set of configuration parameters, framework recommendations, and the reasoning behind each control.

This post introduces our new Linux client hardening guide (MD, PDF), a comprehensive, publicly available hardening reference for Linux systems.

Motivation and Scope

The guide covers the full breadth of controls needed to significantly raise the security posture of a modern Linux installation while preserving operational usability (this will be very subjective, the guide reflects my opinion of “usable”). It has been developed and validated against Ubuntu 24.04 LTS as the primary reference platform, and cross-tested on Fedora, Debian 12, and Arch Linux as well as on traditionally server-oriented distributions like openSUSE Leap 15.6, Debian 12, Rocky Linux 9, and Red Hat Enterprise Linux 9 while not focussing on those as the guide is created for Linux clients.

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After seven years, we’re publishing a new macOS hardening guide. Fully updated, modernized, and now publicly available on GitHub as Markdown and on our website as PDF.

The previous guide, written for macOS Mojave (10.14), reflected a very different macOS security model. At the time, hardening often meant working around the operating system, manually enforcing controls, and compensating for missing platform guarantees. That guide served its purpose, but the platform has fundamentally changed since then.

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The purpose of this blog post is to explain how Secure Boot works. In particular, we will explain where current implementations of Secure Boot by Linux distributors fall short compared to Microsoft Windows and Apple macOS.

Major distributors like Canonical, Debian, openSUSE, and Red Hat place a high priority on making their operating systems work out of the box. Given the current Linux landscape with out-of-tree drivers and incompatible licenses, providing the end user with all the drivers possibly needed to boot the system can be challenging.

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Many Linux hardening guides focus on well-known protections: full-disk encryption, Secure Boot, and password-protected bootloaders. While these measures are critical, they often overlook a subtle but serious attack vector: the ability to drop into a debug shell via the Initial RAM Filesystem (initramfs). This oversight can enable an attacker with brief physical access to bypass conventional boot protections and inject persistent malware into the system.

In this post, it is demonstrated how this attack works on modern Linux distributions, such as Ubuntu and Fedora, and explained why existing guidance often fails to mention it.

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Apple Automated Device Enrollment (ADE) is presented as a way to automate and simplify the enrollment process of Apple devices within Mobile Device Management (MDE) solutions. This blog post is aimed at organizations currently planning or even already using this feature and making you, the reader, aware of potential limitations of this process that might otherwise not be clearly addressed in your companies’ device management process.

How Apple ADE Is Presented

Looking at the Apple Support pages today, Automated Device Enrollment is described as a process that

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Mobile Device Management (MDM) solutions are used to centrally manage mobile devices in corporate environments. This includes the monitoring of the device, automatic installation/removal of apps or certificates and restrict the functionality. Even though MDM solutions exist for multiple vendors, we will look specifically on Apple devices enrolled via Intune. When an Apple device is registered for Automated Device Enrollment (ADE), it will automatically download and apply these policies during the initial setup and prior to the first boot.

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Due to the new release of macOS Mojave in September we updated the El Capitan hardening guide.

The hardening guide received a little revamp on some chapters which are now obsolete or had to be changed due to the new features of macOS Mojave. Further, the hardening guide got extended for the new privacy features in macOS Mojave.

You can check it out here. We hope some of you might find it helpful.
Cheers,
Birk

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During penetration tests, we often find interesting files on web servers. Almost as often, those files enable us to carry out further attacks with much higher impact. Inspired by Chris Gate’s great series From Low to Pwned, we decided to share the following small piece.

The web server under test did not deliver directory listings. However, the directory contained a .DS_Store file (one of macOS’ many — lets say special — traits). While .DS_Store files store various information, a simple cat shows one relevant characteristic:

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Today we started publishing several of our hardening documents to a dedicated GitHub repository — and we’re quite excited about it! It took a while to develop a suitable markdown template to support all the requirements you have when you write a hardening guide, but we’re online now!

At the moment, only a few hardening guides are online, but that should continuously increase in the future.

Click here for the GitHub ERNW Hardening Repository!

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