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Penetration Tester's Open Source Toolkit
By Jeremy Faircloth
SYNGRESS
Copyright © 2011 Elsevier Inc.
All right reserved.
ISBN: 978-1-59749-628-5
Chapter One
Tools of the trade
INFORMATION IN THIS CHAPTER:
• Objectives
• Approach
• Core Technologies
• Open Source Tools
• Case Study: The Tools in Action
• Hands-On Challenge
The quality of the tools that we use as penetration testers is part of what determines the quality of work that we perform. Other parts are, of course, skill, experience, and imagination. By building an excellent toolkit, we can better perform our penetration testing work and do a better, faster, and higher quality job. While the rest of this book will be focusing on individual tools and how to use them, in this chapter we will be talking about toolkits which contain a number of the tools we'll be discussing later and more.
We will also be talking about some of the technologies used to make carrying around your toolkit easier and safer. A good set of tools should always be stored in a good toolbox. In addition, we'll touch on some of the tools that you can use to build target systems for penetration testing. In Chapter 10, we'll talk about building a test lab, but here we'll talk about some of the kits that you can use within that lab.
This chapter may not be quite as interesting as the remaining chapters in this book since we will not be doing any actual penetration testing examples here. However, it is very important to have a solid foundation in the general tools available to you as a penetration tester prior to learning how to use those tools in real-world scenarios. You'll find that it saves you a lot of time later when we demonstrate using a tool if you already have a toolkit which contains it.
1.1 OBJECTIVES
Our objectives for this chapter are to learn which toolkits exist in the open source world for penetration testing, learn how those toolkits are built and how to modify them, and discuss some of the kits which exist to build target systems. To meet these objectives, we'll go over the general approach of how and why these kits are made, then move into the core technologies of how they work. We'll then go over some open source toolkits, which exist today, and talk about how each applies to your work in penetration testing. Lastly, we'll do a case study using one of the available toolkits and give you a chance to show what you've learned in a hands-on challenge.
Many open source penetration testing toolkits exist today and are built to reduce your work. In the past, performing a penetration test meant that every penetration tester built up a set of tools that they prefer using, kept them updated manually, maintained master copies in case of corruption, and had to manually research how to integrate new tools as they became available. This was where a great deal of the penetration tester's time was spent versus getting into the "real" work of testing a client's security. This was generally not considered billable time and was a real challenge.
1.2 APPROACH
The general approach to building penetration testing toolkits is to minimize the amount of work spent maintaining tools and maximize the amount of time spent performing penetration testing. To do this, you generally start with a list of tools that are commonly used for either the specific type(s) of penetration testing that you are performing or a list of tools that can be used for a wide variety of purposes. This is akin to either selecting a knife custom designed for a specific purpose (e.g., a thin bladed knife for filleting) or grabbing a Swiss Army knife to cover a variety of situations.
Generally if you're building your own penetration testing toolkit from scratch, you'll take the approach of selecting your favorite or most commonly used tools. If you are building a toolkit for public use, it's usually best to include a wider variety of tools so that more general penetration testing needs can be met. This is the approach used by most of the people who put together these kits today.
The next decision that you have is the type of operating system that you'd like to use. There are a number of penetration testing tools which are built to run under Windows, but there are typically more tools available under the Linux platform. The challenge there is to determine which Linux distribution to use since there are such a wide variety to choose from. Some examples of popular Linux distributions are:
• Ubuntu
• Fedora
• openSUSE
• Debian GNU/Linux
• Mandriva Linux
• Slackware Linux
• Gentoo Linux
Many of these have served as the foundation for penetration testing toolkits over the years and your choice will often be driven by personal preference as much as any technical reasoning. Each distribution has their own unique release schedule and goals, which may play a part in your decision as well.
With the list of tools and the operating system choice out of the way, now it's time to determine how your penetration test toolkit will execute. Do you want to install the operating system and all tools on a desktop/laptop/etc. permanently or within a virtual machine? Would you prefer to boot off of an optical disk (CD/ DVD)? Or maybe booting and running off of a flash drive or SD card is your preference. Whichever of these options works best for your needs is obviously the direction that you should go. Each has its own pros and cons.
For example, if you choose to do an on-disk installation, you should be aware that any corruption from a bad tool install or an erroneous command could mean reinstalling everything from scratch or restoring from a backup. On the other hand, you can make changes to your toolkit easily and know that those changes will be available for you the next time that you go to use the system. This tends to be a less portable solution, but takes advantage of the speed of the disk and makes saving changes easy.
Booting off of a CD or DVD works great for some toolkits, however, not all operating systems support running in this manner. In addition, you need to be sure that the machine you'll be using has a compatible drive and ensure that your disk doesn't get scratched or otherwise damaged. The risk of corruption is lower since changes are wiped out after the machine using the CD/DVD is powered off, but that also limits your ability to save changes that you actually want to keep such as tool updates.
Using a USB drive or SD card is another option similar to using a CD/DVD, but there are some additional advantages and disadvantages here. Not all systems support booting off of a USB drive and even fewer support booting off of an SD card so compatibility can be a problem. However, with correct partitioning, you can build a USB/SD penetration testing toolkit which supports persistent changes, meaning that all modifications that you make to the booted OS are saved to a special partition and reapplied the next time the toolkit is booted up. This is considered a "persistent Live USB" build and has the advantage of being able to be returned to a baseline state by removing the persistence partition. Alternately, you can build an operating system on the USB drive that is read/write like a normal hard disk.
Whether you're installing on a drive or building a bootable image, your next step is to install your tools. Many of the open source tools available share dependencies and in some cases conflict on the version of those dependencies that they support. While you may want to use the latest version of a specific driver, for example, there may be something new in that version that your chosen tools don't support. Always keep this in mind when doing your tool installations. The process of resolving incompatibilities and ensuring that the correct dependencies are there is very time consuming and requires a lot of effort.
1.3 CORE TECHNOLOGIES
There are a few core technologies that you need to be aware of when building your penetration testing toolkit. In this section, we'll talk about LiveCDs and how they work as well as some basics on how to build or modify a LiveCD. We'll talk about International Organization for Standardization (ISO) images and how to use those as well. Next, we'll go over how to make a bootable USB drive and then finish up by talking about how to make a persistent LiveCD environment.
1.3.1 LiveCDs
A LiveCD is basically a CD or DVD that is written with a bootable version of an operating system modified so that there is no need to write files to the disk the system is booted from. This allows you to use read-only media to boot a system into a fully functional operating system, leaving no data written to the hard disks of the system that you're using. It isn't even required for the system to have a hard disk since everything it needs will be coming off of the optical media.
LiveCDs started becoming popular in the early to mid 1990s and it's now common to find LiveCDs that support a majority of the common operating systems or distributions. Since most operating systems do need a place for temporary files, LiveCDs are built to create this temporary file area in memory or (less commonly) use an existing location on the system's hard disk. Files created while using the LiveCD that the user wants to keep can usually be written to a USB drive or a hard disk partition as well.
1.3.1.1 Creating a LiveCD
Depending on the operating system that you're using, a number of options exist on how to create your LiveCD. For Windows, one of the most popular methods of creating a LiveCD is to use Bart's Preinstalled Environment (BartPE) Builder to create a Windows-based bootable CD or DVD. This is free software and is available at http://www.nu2.nu/pebuilder/. Using BartPE in combination with an original licensed Microsoft Windows DVD allows you to generate a bootable image very quickly and easily. We'll demonstrate the use of this tool in the Open source tools section of this chapter.
Creating a LiveCD with Linux is a little more complex and can vary depending on distribution. For Ubuntu, this involves creating a number of directories and installing some packages on an existing Linux system, creating a copy of the operating system, modifying it to work properly, building out the appropriate directory structures, then finally burning the CD or DVD. All of the steps and a detailed tutorial on this process can be found at http://ubuntuforums.org/showthread.php?t=688872.
Using Fedora, the process is a little more streamlined. There is a LiveCD-tools package available which includes a tool called LiveCD-creator. This tool effectively goes through the following steps:
• Sets up a file for the ext3 file system that will contain all the data comprising the LiveCD
• Loopback mounts that file into the file system so there is an installation root
• Bind mounts certain kernel file systems (/dev, /dev/pts, /proc, /sys, /selinux) inside the installation root
• Uses a configuration file to define the requested packages and default configuration options. The format of this file is the same as is used for installing a system via kickstart.
• Installs, using yum, the requested packages into the installation using the given repositories in the kickstart file
• Optionally runs scripts as specified by the LiveCD configuration file
• Relabels the entire installation root (for SELinux)
• Creates a LiveCD-specific initramfs that matches the installed kernel
• Unmounts the kernel file systems mounted inside the installation root
• Unmounts the installation root
• Creates asquashfs file system containing only the defaultext3/4file (compression)
• Configures the boot loader
• Creates an iso9660 bootable CD/DVD
This greatly simplifies the LiveCD creation process if Fedora is the distribution that you are using. Full documentation on this process is available at http:// fedoraproject.org/wiki/How_to_create_and_use_Fedora_Live_CD.
1.3.1.2 Modifying LiveCDs
Modifying LiveCDs is very similar to creating a LiveCD from scratch except that you have an easier foundation to work from. Basically, the contents of the LiveCD are extracted into a working area and modified as needed. This can include the addition of new files, modification of existing files, or deletion of files as required. Where this becomes complex is when you need to perform installations of packages and then build a new LiveCD using the updated versions.
To do this, there are a couple of methods that you can use. First, you can perform an install of the operating system to a machine, update all of the files or packages necessary, and then rebundle that modified version as a new LiveCD. Alternately, you can take the compressed images created when building some types of LiveCDs, mount those images, update them, and then use the updated images to create a new LiveCD. This is generally the method used with Knoppix as an example. An example of a similar method for Ubuntu can be found at https://help .ubuntu.com/community/LiveCDCustomization.
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Excerpted from Penetration Tester's Open Source Toolkit by Jeremy Faircloth Copyright © 2011 by Elsevier Inc.. Excerpted by permission of SYNGRESS. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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