Saturday, December 15, 2012

There are FOUR lights!

Okay, you're probably wondering what Picard and one particular episode of Star Trek TNG has to do with forensicating.  Well, to put it quite simply...everything!

I recently posted the question in a forum regarding Shellbag analysis, and asked who was actually performing it as part of their exams.  One answer I got was, "...I need to start."  When I asked this same question at the PFIC 2012 conference of a roomful of forensicators, two raised their hands...and one admitted that they hadn't done so since SANS training.

I've seen during exams where the shellbags contain artifacts of user activity that are not found anywhere else on the system.  For example, I've seen the use Windows Explorer to perform FTP transfers (my publisher used to have me do this to transfer files), where artifacts of that activity were not found anywhere else on the system.  When this information was added to a timeline, a significant portion of the exam sort of snapped into place, and became crystal clear.

Something I've seen with respect to USB devices that were connected to Windows systems is that our traditional methodologies for parsing this information out of a system are perhaps...incomplete.  I have seen systems where some devices are not so much identified as USB storage devices by Windows systems (rather, they're identified as portable devices...iPods, digital cameras, etc.), and as such, starting by examining the USBStor subkeys means that we may miss some of these devices that could be used in intellectual property theft, as well as the creation and trafficking of illicit images.  Yet, I have seen clear indications of a user's access to these devices within the shellbags artifacts, in part because of my familiarity with the actual data structures themselves.

The creation and use of these artifacts by the Windows operating system goes well beyond just the shellbags, as these artifacts are comprised of data structures known as "shell items", which can themselves be chained together into "shell item ID lists".  Rather than providing a path that consists of several ASCII strings that identify resources such as files and directories, a shell item ID list builds a path to a resource using these data structures, which some in the community have worked very hard to decipher.  What this work has demonstrated is that there is a great deal more information available than most analysts are aware.

So why is understanding shell items and shell item ID lists important? Most of the available tools for parsing shellbags, for example, simply show the analyst the path to the resource, but never identify the data structure in question...they simply provide the ASCII representation to the analyst.  These structures are used in the ComDlg32 subkey values in the NTUSER.DAT hive on Windows Vista and above systems, as well as in the IE Start Menu and Favorites artifacts within the Registry.  An interesting quote from the post:

Of importance to the forensic investigator is the fact that, in many cases, these subkeys and their respective Order values retain references to Start Menu and Favorites items after the related applications or favorites have been uninstalled or deleted.

I added the emphasis to the second half of the quote, because it's important.  Much like other artifacts that are available, references to files, folders, network resources and even applications are retained long after they've been uninstalled or deleted.  So understanding shell items are foundational to understanding larger artifacts.

But doesn't stop with the item ID lists are part of Windows shortcut (LNK) files, which means that they're also part of the Jump Lists found on Windows 7 and 8.

Okay, but so what, right?  Well, the SpiderLabs folks posted a very interesting use of LNK files to gather credentials during a pen test; have any forensic analysts out there seen the use of this technique before?  Perhaps more importantly, have you looked for it?  Would you know how to look for this during an exam?

Here's a really good post that goes into some detail regarding how LNK files can be manipulated with malicious intent, demonstrating how important it is to parse the shell item ID lists.

So, the point of the graphic, as well as of the post overall, is this...if you're NOT parsing shellbags as part of your exam, and if you're NOT parsing through shortcut files as part of your root cause analysis (RCA), then you're only seeing three lights.

There are, in fact, four lights.

DOSDate Time Stamps in Shell Items
ShellBag Analysis, Revisited...Some Testing

1 comment:

Anonymous said...

I just read your post and wanted to provide a little feedback. Because of your previous posts concerning Shellbags and their importance to forensics, I decided to do a little research. Of course my employer, an agency, requires a research project for advancement I decided to research shellbags. I use shellbag analysis on each and every case I have a windows installation. I also use regripper, bulk extractor and timeline analysis. Thanks for Tapeworm. You can find shellbags in volume shadow copies and I've had a case where more then 5000 shellbags were observed. My research goes from what are shellbags to using the various mainline forensic tools to find/examine shellbags to using not so mainline tools (sbag64, etc...). I wanted to show/tell a story of shellbags. From my two instructor tours in the US Navy, I'm writing to a level I hope everyone can understand and using tons of graphic/screen captures. I they can't read and understand it, maybe the picture will get the point across.