Hypothetical: Imagine that you visit your local mall and browse around for stuff to buy. And you decide to buy a new CD from your favorite artist and you also buy a brand new cool USB stick thingy on an impulse. You go home and stick the CD into your laptop's CD drive. It prompts you to install some software. You do so and while you are listening to the music, you open the USB stick package and start experimenting with your new toy. It has a fingerprint reader so you install the software for that as well. Guess what… you might have just installed, not one, but two different rootkit-like software on your laptop.
We received a report that our F-Secure DeepGuard HIPS system was warning about a USB stick software driver. The USB stick in question has a built-in fingerprint reader. The case seemed unusual so we ordered a couple of USB sticks with fingerprint authentication. We installed the software on a test machine and were quite surprised to see that after installation our F-Secure BlackLight rootkit detector was reporting hidden files on the system.
Many of our regular readers will remember the huge Sony BMG XCP DRM rootkit debacle of 2005. Back then malware with rootkits were not very common but since then a lot of malware families have adopted rootkit cloaking techniques. It is unclear if the "rise of the rootkit" would have happened in this magnitude without the publicity of the Sony BMG case. In any case, a lot more people now know what a "rootkit" is than back then.
This USB stick with rootkit-like behavior is closely related to the Sony BMG case. First of all, it is another case where rootkit-like cloaking is ill advisedly used in commercial software. Also, the USB sticks we ordered are products of the same company — Sony Corporation.
The Sony MicroVault USM-F fingerprint reader software that comes with the USB stick installs a driver that is hiding a directory under "c:\windows\". So, when enumerating files and subdirectories in the Windows directory, the directory and files inside it are not visible through Windows API. If you know the name of the directory, it is e.g. possible to enter the hidden directory using Command Prompt and it is possible to create new hidden files. There are also ways to run files from this directory. Files in this directory are also hidden from some antivirus scanners (as with the Sony BMG DRM case) — depending on the techniques employed by the antivirus software. It is therefore technically possible for malware to use the hidden directory as a hiding place.
In addition to the software that was packaged with the USB stick, we also tested the latest software version available from Sony at www.sony.net/Products/Media/Microvault/ and this version also contains the same hiding functionality.
It is our belief that the MicroVault software hides this folder to somehow protect the fingerprint authentication from tampering and bypass. It is obvious that user fingerprints cannot be in a world writable file on the disk when we are talking about secure authentication. However, we feel that rootkit-like cloaking techniques are not the right way to go here. As with the Sony BMG case we, of course, contacted Sony before we decided to go public with the case. However, this time we received no reply from them.
It should be noted that MicroVaults with fingerprint authentication appear to be an older product and may no longer be manufactured. At least we had some trouble finding a reader of this type in Helsinki. Nevertheless, we did manage to find them on sale.