(Almost) undetectable hardware-based rootkits

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.

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