Using Hard-Drive Imaging In Forensics

A client recently asked me about adding hard drive imaging into its standard incident response process. Because most of the incidents the client deals with are related to malware infections, its current process is to make sure the user's data is backed up before wiping the hard drive and installing a fresh version of the operating system -- a solid process, but it could use some improvements to deal with modern malware.The client's inquiry came as a result of several infections that involved data-stealing malware like Zeus, which has been seen to steal banking credentials and documents from infected systems (see "Government Employees Targeted By Zeus Trojan"). Its goal was to increase its speed and effectiveness by imaging Windows physical memory and the system's hard drives before destroying valuable evidence. After imaging, it would proceed as usual with wiping and OS installation while analysis of the images could be performed concurrently, or as time permitted, to determine if sensitive information was on the drive and possibly the target.

I covered Windows memory imaging tools a couple of weeks ago, so if you missed it, here's the link: "Acquiring Windows Memory For Incident Response." For hard drive imaging, there are tons of options, including software and hardware solutions. What you choose will most commonly depend on the hard drive (interface and size), how much time you have to image the drive, and whether the system must stay online.

Personally, I prefer to use a hardware-based imaging device because it is often much faster than software tools and can image disk-to-disk and disk-to-file, perform disk hashing, format and wipe disks, and more. I've used the Tableau TD1, and it works great, but there are other products I've heard good things about, like the Voom HardCopy. Using a hard drive imager is great in those situations when you need to get in and get out as quick as possible.

On the software-based front, imaging can be done using numerous software tools with either hardware or software write blockers that prevent the hard drive from being modified during the imaging process. Hardware write blockers are available from several different vendors including Tableau and WiebeTech. I primarily use the ones from Tableau. They can connect hard drives of all types (PATA, SATA, SCSI, etc.) for imaging and analysis via USB, Firewire, and eSATA. Once connected, the hardware prevents all writes to the hard drive keeping the original evidence "forensically sound."

With the hardware write blockers, the most common tools for imaging are FTK Imager, EnCase, dd, and X-Ways Forensics. I typically will use FTK imager because it offers a variety of formats for outputting the hard drive image, including raw (or dd), EnCase, and FTK compatible types. It can also convert between different formats, image Windows memory, collect the live Windows Registry from a running system, and it's free from the AccessData Downloads page.

Tableau recently released Tableau Imager, a software imaging tool to use with its hardware write blockers that is supposed to speed up the imaging process. In some quick tests, it did prove a faster than FTK Imager, but about the same as X-Ways Forensics. The SANS Forensics Blog has a post with some more information about the Tableau Imager, and one reader's comments included his test imaging speeds with various tools.

That's a ton of information already on hard drive imaging, with still a lot to cover on the software write blocking side. On Wednesday, I'll cover some of the popular tools for software write blocking, like F-Response and Encase, and the functionality included in CAINE and Helix3 Pro.

John H. Sawyer is a senior security engineer on the IT Security Team at the University of Florida. The views and opinions expressed in this blog are his own and do not represent the views and opinions of the UF IT Security Team or the University of Florida. When John's not fighting flaming, malware-infested machines or performing autopsies on blitzed boxes, he can usually be found hanging with his family, bouncing a baby on one knee and balancing a laptop on the other. Special to Dark Reading.