Hardening on Insinuator.net - Bold Statements

ERNW White Paper 77: Unified Security Hardening with Cross-Platform Native Binaries

Wed, 20 May 2026 00:00:00 +0000

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

ERNW Whitepaper 76: Linux Client Hardening Guide

Tue, 19 May 2026 00:00:00 +0000

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.

One More Thing: Introducing the New macOS 26 Tahoe Hardening Guide

Wed, 11 Feb 2026 00:00:00 +0000

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.

Setting up Secure Boot on Gentoo Linux

Mon, 28 Jul 2025 00:00:00 +0000

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.

Insecure Boot: Injecting initramfs from a debug shell

Thu, 03 Jul 2025 00:00:00 +0000

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.

Disclosure: Potential Limitations of Apple ADE in Corporate Usage Scenarios

Tue, 03 Sep 2024 00:00:00 +0000

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

Disclosure: Apple ADE – Network Based Provisioning Bypass

Fri, 09 Aug 2024 00:00:00 +0000

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.

macOS Mojave Hardening Guide

Thu, 10 Jan 2019 00:00:00 +0000

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

Files Your Webserver Shouldn’t Deliver

Sun, 18 Sep 2016 00:00:00 +0000

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:

ERNW Hardening Repository

Sun, 21 Aug 2016 00:00:00 +0000

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!

Internet Information Service 7.5 Hardening Guide

Fri, 26 Jun 2015 00:00:00 +0000

Internet Information Services (IIS) contains several components that perform important functions for the application and Web server roles in Windows Server. As it is designed to be used in an enterprise environment, the security of this system must be kept at a high level.

By default IIS implements a lot of basic security measures, but are these the relevant ones to protect your business?

In order to answer this question for one of our customers, we have compiled the most relevant security settings in an IIS 7.5 Hardening Guide for you. In this guide we define a baseline security level, which is to be used for so called “crash and burn systems” (systems with non-critical data, systems whose availability have no business relevant impact) and a security level high, which includes all other systems. The mitigations in the baseline section are non-critical and therefore no further test are necessary. The mitigation in the section high, are critical in terms of availability and need to be tested extensively. The system owner must decide, which security level is the right one for their system, and which mitigation from section high are mandatory for their system.

IPv6 Hardening Guide for OS X

Wed, 04 Feb 2015 00:00:00 +0000

Similar to the documents we released for Linux and Windows (and actually inspired by a comment to the post on the Linux guide) Antonios wrote another guide, this time for Mac OS X.

It can be found here. We hope some of you might find it helpful.
Have a great day

Enno

PS: in the past we also made a general Mac OS X hardening document available and we’ve discussed an additional patch in this post.

Hardening Against Local PrivEsc: Protecting Your Links

Tue, 30 Dec 2014 00:00:00 +0000

Following up on this post, we want to provide some details on two rather new (well, compared to its lifespan) Linux kernel parameters — and emphasize the need to enable those:

fs.protected_hardlinks
fs.protected_symlinks

For BSD, similar parameters for hardlinks exist: security.bsd.hardlink_check_uid/security.bsd.hardlink_check_gid.

Those parameters control whether users are allowed to create links pointing to files which are not owned by them. If fs.protected_hardlinks/symlinks is set to 1, users can only create links to files which they own. Attackers have used this possibility for a long time, and here are some sample attack scenarios:

IPv6 Hardening Guide for Windows Servers

Mon, 22 Dec 2014 00:00:00 +0000

After we recently released the “Linux IPv6 Hardening Guide” we got a number of suggestions “could you pls provide a similar document for $OS?” (btw: thanks to you all for the overwhelming interest in the Linux document and the active discussion of ip6tables rule approaches on the ipv6hackers mailing list).

Hence Antonios thankfully decided to put together a list of configuration steps for Windows servers. It can be found here.

Once more we’d like to emphasize that the approach described is only suited for very specific environments with high security requirements and an associated ratio of “generous operational resources”. From our perspective this guide is intended mostly to serve as a source of inspiration (“what could be done”) and for documentation purposes (“how to do it”). Everything described should be carefully tested in your specific environment.
For example, we were recently involved in IPv6 security planning in an organization where the Windows guys (completely legitimately) came up with a stance of “before we fully accept and ratify the strategy and policy just discussed, we’d like to get feedback from Microsoft, if we still have full support once we follow this path”.

IPv6 Hardening Guide for Linux Servers

Wed, 17 Dec 2014 00:00:00 +0000

We were recently approached by a customer asking us for support along the lines of “do you have any recommendations as for strict hardening of IPv6 parameters on Linux systems?”. It turned out that the systems in question process quite sensitive data and are located in certain, not too big network segments with very high security requirements.

They indicated they were willing to spend significant operational resources on “securely configuring them”. So Antonios deciced to write a small hardening guide for IPv6 on Linux, mostly focusing on manual configuration of pretty much everything (including neighbor cache entries 😉 with accompanying deactivation of all automatic mechanisms, together with ip6tables based local packet filtering.
The document can be found here.

Tomcat 7 Hardening Guide

Sat, 11 Jan 2014 00:00:00 +0000

Hi,

continuing our tradition from last year (see here and here), we summarized more of our hardening recommendations for you. This guide is covering Tomcat 7 and is supposed to provide a solid base of hardening measures. It includes configuration examples and all necessary commands for each control, specifically for the most recent branch of Tomcat as there were some significant changes. Download: ERNW_Checklist_Tomcat7_Hardening.pdf

Have a good one,

Matthias

SLES 11 Hardening Guide

Thu, 15 Aug 2013 00:00:00 +0000

SUSE Linux Enterprise Server (SLES) has been around since 2000. As it is designed to be used in an enterprise environment the security of these systems must be kept at a high level. SLES implements a lot of basic security measures that are common in most Linux systems, but are these enough to protect your business? We think that with a little effort you can raise the security of your SLES installation a lot.

Basic OS X Hardening & DMA

Wed, 31 Jul 2013 00:00:00 +0000

In the course of a recent endpoint assessment, we also had a OS X 10.8 client system as a target. While we still rely on the Firewire “capability” of unlocking systems on a regular base (using this great tool), we noticed that Apple released a patch to disable Firewire DMA access whenever the system is in a locked state (e.g. with an active screensaver or no user logged in). As we test the Firewire DMA access vulnerability quite often (at least we thought so 😉 ) to prepare for demonstrations in the board room or client assessments, we were quite surprised that we must have actually missed that nice update. In order to verify the effectiveness of the patch, we ran our typical test bed and can quite happily confirm that the update successfully mitigates Firewire DMA access in locked system states.

iOS Hardening Configuration Guide

Sun, 17 Jul 2011 00:00:00 +0000

Hi everybody,
eye-catching title of this post, huh?

Actually there is some justification for it ;-), that is bringing this excellent document covering the exact topic to your attention.
Other than that this post contains some unordered reflections which arose in a recent meeting in a quite large organization on the “common current iPad topic” (executives would like to have/use an iPad, infosec doesn’t like the idea, business – as we all know – wins, so bring external expertise in “to help us find a way of doing this securely” yadda yadda yadda).
Which – given those nifty little boxes are _consumer_ devices which were probably never meant to process sensitive corporate data – might be a next-to-impossible task… at least in a way that satisfies business expectations as for “usability”…[btw: can anybody confirm my observation that there’s a correlation between “rigor of restriction approach” to “number of corporate emails forwarded to private webmail accounts”?]

Once more: hardening is better than patching

Wed, 13 Apr 2011 00:00:00 +0000

I can’t help myself. And I fully understand that some of you, dear readers, might get a bit annoyed by always hearing the same tune from our side. This post is, surprise!, about yesterday’s Microsoft Patch Tuesday which – as can be seen here and here – disclosed quite a number of vulnerabilities in various Microsoft components. To make the point evoked in this post’s title I’d like to draw your attention to two particular bulletins, both rated as critical.

News from the Desktop, Edition 2010/07/21

Wed, 21 Jul 2010 00:00:00 +0000

Back on track as for one of our favorite rant subjects: desktop security. This stuff, commonly called the “LNK vulnerability”, has gained quite some momentum in the last days, including the release of a Metasploit module and a temporary raise of SANS Internet Storm Center‘s Infocon level to yellow (it’s back on green in the interim).

CVE-2010-2568 has been assigned and some technical details can be found here and here.

To give you a rough idea how this piece works, here’s a quote from the US-CERT advisory:

News from Old Friends, Edition 2010/06/09

Wed, 09 Jun 2010 00:00:00 +0000

This is the first post of a – potential – series of rants on ubiquitous pieces of crap (security-wise), bothering pretty much every ISO I know.
I’m talking about “common desktop applications” and today’s topic is going to be the beloved Adobe Flash Player. Some of you who had the opportunity (or imposition 😉 to listen to one my talks covering “modern enterprise security space” (e.g. this one) might remember me saying sth like “If a fairy godmother turned up and asked me for three things to get rid of in order to enhance overall corporate information security in a sustainable way, my answers would be…” and then giving Adobe Flash as the first mention. (before you ask: amongst the other candidates are Apple Quicktime, Windows GDI and “Javascript in Acrobat Reader”).