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15.1. Your Personal Virus Analysis Laboratory

One of the most important requirements of malicious code analysis is the installation of a dedicated virus analysis system. It is vital that such systems be connected only to "dirty" networks (other systems that are used for similar purposes). Trust me on thisyou do not want to analyze virus code on a production network! A system that is used to replicate virus code should not be used for any other task, and it needs to be restored to a clean state on a regular basis, preferably after each individual test.

There are two basic choices for a dedicated system. I suggest a combination of these:

  1. The first possibility is based on the use of real systems, such as two regular PCs that can run a set of various operating systems fast enough. The PCs can be restored to a known state from backups. It is important to restore the clean test systems very quickly. I suggest that you use a system such as Norton Ghost to save the images of installed operating systems, such as Windows XP, and restore these from a read-only medium like a CD-ROM. It is best to preinstall your analytical tools on the system, but just in case, keep them on a CD also so you can run them from there if the malware should compromise or delete them on the hard disk.

    Note

    To analyze most computer worms effectively, you need at least two such PCs. In one particular installation, one of the analysis PCs might run a vulnerable Apache Server on Linux, and another analysis PC might be used to run a worm, such as Linux/Slapper. As the worm scans for new targets, you might be able to log the network activity with a tool such as tcpdump. Then you can reconfigure the network interface of the target system on the fly so the worm will naturally and quickly find and infect it. This technique works effectively if the worm uses linear IP scanning.


  2. The second option is to use virtual PC software, such as the excellent VMWARE or Virtual PC of Microsoft. VMWARE can run nonpersistent images of guest operating systems. This allows quick, clean restarts of a variety of host operating systems without extra hassle.

Another possible method is to use your own virtual machine based on code emulation and run this on either of the preceding configurations. Good antivirus systems come with virtual machines to emulate modern processor and operating systems. These emulators and their extended versions can be used to build a dedicated virtual machine for virus analysis. Such a tool can be extremely valuable in dealing quickly and safely with antidebugging, encrypted, polymorphic, metamorphic, and packed malicious code. I will illustrate this with VAT (Virus Analysis Toolkit), which we built at Data Fellows in Finland in 1997.

The VMWARE-based method is quickly becoming a standard choice of many researchers. However, certain threats do not work in VMWARE environments. For example, some viruses, such as W95/CIH, which were highly successful in real environments2, fail to work on VMWARE. Furthermore, the virtual environments can be detected by the malicious code, which might act against it. Nevertheless, VMWARE is an invaluable test environment, and I strongly suggest that you buy it. It will pay for itself by reducing the overall hardware costand it makes the process of returning to a clean state much faster.

VMWARE also has network-oriented versions, such as VMWARE GSX Server. GSX Server allows you to run a single VMWARE server, which can have several network clients running images from it at once.

In VMWARE, you can even have your own DNS server and define systems with the names of real companies. This means that you can capture a DoS attack in action against www.microsoft.com, for exampleall in the virtual world.

The goal however, must be the easy administration of such a system. An overly large system is very difficult to manage. Another problem appears because many of the modern threats are vulnerability-dependent. Thus if you only have images that are patched, some computer worms will not work on your system. This can become painful, because the installation of VMWARE environments can take more time than the installation of real systems. The solution is the preparation of a diversified set of VMWARE images with software that is commonly attacked by malicious code. Different flavors of Microsoft IIS servers and Apache servers are a good start, but you cannot experience computer worms such as W32/CodeRed or Linux/Slapper without installing the vulnerable software that is exploited by a particular worm.

In Chapter 3, "Malicious Code Environments," I illustrated that malicious code can depend on a particular environment. To analyze a particular class of computer viruses, such as macro or script viruses, you need the appropriate client software installed, such as Microsoft Office systems. Similarly, more and more malicious code will be written in MSIL, which currently requires the .NET Framework to be installed to run on most Windows systems. I also pointed out in Chapter 3 that some threats depend on the actual file system of a particular target operating system. For example, if you only have FAT systems, viruses that use NTFS streams3 cannot work completely (or at all) on your dedicated system. Thus you need to take care of the diversification of the environments at all levels, from the appropriate hardware to the necessary software.

15.1.1. How to Get the Software?

Systems like this can become rather expensive to build. You can limit yourself to operating systems that are free or cheap, but you also need the environments in which most malicious code currently operates at large, and nowadays that is the Windows platform. Where can you find the systems to install, then? A subscription to MSDN is definitely a good start. Microsoft will send you all the environments you ever need to analyze malicious code on Windows platforms. For instance, if you need a vulnerable version of Microsoft IIS, you will have it in MSDN. Need a release of SQL Server 2000 installation for another worm or exploit to analyze? You've got it in MSDN.

Beta programs to new operating systems are another effective way to get involved in new environments more quickly. Using betas allows you to gain a better understanding of the operating systems early on. In fact, if you are fortunate, you might work for the IT response team of a large corporation. In such a situation, you often get access to new hardware environments, such as 64-bit Windows operating systems on the IA-64 platforms, letting you research platforms earlier than the bad guys. Taking a look at beta boards and OS versions gives you the knowledge you will need when the threats to such platforms become real. It is always good to be ahead of time, learning as much about new platforms as possible. The more you learn about such environments, the better your chances of analyzing applications written for them. It is the environmentnot the malicious codethat is the difficult part to understand.

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