(Almost) undetectable hardware-based rootkits
Fourth-Generation Rootkits
![](/var/linux_magazin/storage/images/linux-magazine.com/issues/2008/97/fourth-generation-rootkits/insec.png/428642-1-eng-US/insec.png_medium.png)
We look at the history of the rootkit, including its newest incarnation, the DR RootKit.
Originally, I intended to write an article about the current state of rootkits and the tools that could be used to detect them. But I ran into a slight problem – the more modern rootkits tend to be really good at avoiding detection. By really good, I mean that you're unlikely to detect them unless you take action, such as a detailed analysis of a system memory dump, for example, comparing the actual kernel image with the expected.
History Lesson
Traditional rootkits were relatively simplistic programs, often running as a standalone daemon providing backdoor access. These were generally easy to detect by looking for a new process or newly installed software, which led attackers to start subverting system binaries. In turn, this led to attackers installing modified system binaries, such as hacked versions of OpenSSH that have a hard-coded administrative username and password to get root-level access. With the advent of tools such as Tripwire and the increasingly common use of package managers that can verify the integrity of installed files, such as RPM and dpkg, these became easy to detect [1].
Kernel-Based Rootkits
Soon attackers realized that more sophisticated hiding and subversion methods were needed to control a system, which led to kernel-based rootkits. By modifying the system call table, an attacker can avoid detection easily because, simply put, they control what you are seeing and how your programs are executing.
Typically attackers use one of two methods to modify the system kernel: either loading a malicious kernel module (e.g., heroin) or patching the in-memory kernel by writing to the special device /dev/kmem (e.g., SucKIT). Because these attacks live in memory only, their disadvantage is that they typically do not survive a reboot.
Difficult as they can be to detect, these rootkits can be found by comparing the current system call table with the expected (i.e., by examining the file System.map). Dumps of system memory can be taken and used to verify that the kernel in memory is correct.
So what are attackers to do? Go deeper, of course.
Hardware-Based Rootkits and the Virtualized OS
Released in 2006 at Black Hat in Vegas, the first publicized hardware-based rootkit was called "Blue Pill" [2]. Modern CPU's from AMD and Intel include a number of features that support virtualization of operating systems. Because they no longer need to modify the operating system to work, these rootkits are harder to detect, so checking your system call table won't work. However, these rootkits do replace the Interrupt Descriptor Table (IDT), which is held within a CPU register (the IDTR) [3].
Because two IDTRs (the real one and the one being presented to the compromised operating system) now exist, the one being presented to the compromised operating system will be at a different memory location than usual. Fortunately, the privileged instruction Store Interrupt Descriptor Table (SIDT) can be run from user space and will reliably return the contents of the IDTR being presented to the operating system (which isn't very helpful because it has been compromised) and, more importantly, the memory location (which won't be in the normal location).
This appears to be a stalemate: The attackers have created new methods to hide rootkits, and the defenders have found ways to detect them.
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
![Learn More](https://www.linux-magazine.com/var/linux_magazin/storage/images/media/linux-magazine-eng-us/images/misc/learn-more/834592-1-eng-US/Learn-More_medium.png)
News
-
NVIDIA Released Driver for Upcoming NVIDIA 560 GPU for Linux
Not only has NVIDIA released the driver for its upcoming CPU series, it's the first release that defaults to using open-source GPU kernel modules.
-
OpenMandriva Lx 24.07 Released
If you’re into rolling release Linux distributions, OpenMandriva ROME has a new snapshot with a new kernel.
-
Kernel 6.10 Available for General Usage
Linus Torvalds has released the 6.10 kernel and it includes significant performance increases for Intel Core hybrid systems and more.
-
TUXEDO Computers Releases InfinityBook Pro 14 Gen9 Laptop
Sporting either AMD or Intel CPUs, the TUXEDO InfinityBook Pro 14 is an extremely compact, lightweight, sturdy powerhouse.
-
Google Extends Support for Linux Kernels Used for Android
Because the LTS Linux kernel releases are so important to Android, Google has decided to extend the support period beyond that offered by the kernel development team.
-
Linux Mint 22 Stable Delayed
If you're anxious about getting your hands on the stable release of Linux Mint 22, it looks as if you're going to have to wait a bit longer.
-
Nitrux 3.5.1 Available for Install
The latest version of the immutable, systemd-free distribution includes an updated kernel and NVIDIA driver.
-
Debian 12.6 Released with Plenty of Bug Fixes and Updates
The sixth update to Debian "Bookworm" is all about security mitigations and making adjustments for some "serious problems."
-
Canonical Offers 12-Year LTS for Open Source Docker Images
Canonical is expanding its LTS offering to reach beyond the DEB packages with a new distro-less Docker image.
-
Plasma Desktop 6.1 Released with Several Enhancements
If you're a fan of Plasma Desktop, you should be excited about this new point release.