Kernel Trouble

This deep look at how intruders attack an out-of-date kernel should be enough to convince you of the need to stay vigilant.

- Chris Binnie

The multitudinous varieties of attacks that can affect OSs are hard to keep up with, but recently I wanted to test some Linux kernel exploits to keep up with my interest in ethical hacking. Such attacks often occur once access has been gained to a system. They are sometimes used in order to achieve privilege escalation – in other words, to boost a non-root user's privileges to the level of the root user in order to gain full control of the system.

It is easy to become content with the kernel you are running and forget to install all the updates and upgrade the system when the kernel is no longer supported. Many users install long-term support (LTS) Linux systems and get so used to them after five years that they aren't in a hurry to upgrade when the service cycle ends.

This article will introduce you to some techniques intruders use to attack old kernels, and, in case you ever had any doubts, it should convince you to never fall behind on those kernel patches and updates.

To test these exploits, I needed a lab that wouldn’t cause me any associated security concerns. In this article, I’ll show you how to set up a flexible but simple lab that you can easily re-use and archive through snapshots to save your progress. Then, I’ll demonstrate how to run a kernel exploit against a vulnerable machine and, finally, how to install much older versions of the Linux kernel that you can boot into, so you can pick and choose which known vulnerabilities to practice against. It should go without saying: Only use these tools and methods on systems that you own or that you have been explicitly given permission to test against.