Tuesday, April 10, 2012

Value of Targeted Timeline Analysis in Research

I recently conducted some research into a specific event/activity on a system, and found that timeline analysis proved to be an extremely valuable technique to use in this case.  I see a good number of questions online in the various forums asking about what could lead to a particular event, and in most cases, I ask the poster if they'd considered generating a timeline.  After all, any time you're interested in an event that occurred, particularly one that occurred at a specific time, generating and analyzing a timeline is a great way to answer that question.  It's also a great way to conduct analysis as part of research.

As indicated in my previous post, I had read online that the volume GUIDs found in the value names within the MountedDevices key, as well as within a user's MountPoints2 subkey names follow the UUID v1 format discussed in RFC 4122.  As such, this GUID contains a node identifier, which is most often a MAC address from the system.  Okay, that's easy enough.  There is also a 60-bit time stamp embedded in the GUID, which tracks 100 nano-second intervals since 15 Oct 1582...and I got interested in determining to what event that time stamp referred or was associated, specifically on my Windows 7 Ultimate test system.

I purchased a SanDisk Blade thumb drive (it was on sale), as I knew that such a device had never been connected to my system.  I then recorded the time and date that I booted system, as well as when I first connected the device to the system.  After connecting the device and noting the drive letter to which it was mapped, I disconnected it, waited a couple of hours and reconnected the device.  After disconnecting it, I shut the system down.  Again, I recorded the significant times in my notes.

Several days later, I copied the setupapi.dev.log file, extracted the System, Software, and NTUSER.DAT hives via FTK Imager, and dumped the System Event Log via LogParser, using the following command:

logparser -i:evt -o:csv "Select RecordNumber,TO_UTCTIME(TimeGenerated),EventID,SourceName,Strings from System" > d:\cases\local\system.csv

Using the appropriate tools, I generated my events file in preparation for creating a timeline.  I wrote a specific script to parse the System Event Log entries into the necessary five-field format, and crafted a specific variant of the RegRipper mp2.pl plugin to parse the volume GUIDs based on the UUID v1 time stamps.  I used regtime.pl (part of my timeline tools) to parse the Registry hives into the necessary format.

Now, what I didn't do was create a supertimeline from all data sources, as it wasn't necessary to do so.  No new Prefetch files had been created during the testing process, and I hadn't created or edited files on the thumb drive, so there really was no need to collect file system metadata.  I focused solely on the System Event Log as I understand that a number of event records are created in that log file with respect to drivers and USB devices, as well as a number of system-specific records.

What I was able to determine is that the time stamp within the volume GUID refers to the boot time of the boot session during which the device was connected to the system.  For example, I booted my test system at approximately 4:29pm EDT on 4 April 2012 (as indicated by a Microsoft-Windows-Kernel-General record with event ID 12); however, I didn't plug the device into the system until 4:55pm EDT (remember, I disconnected it and then plugged it again later at 9:02pm EDT).  When I parsed the volume GUID for the time stamp and normalized it to 32-bit time format, the time was within a second of the boot time of the system.  Throughout the rest of the timeline, I saw the creation of keys beneath the Enum\USB and Enum\USBStor keys within the System hive, as well as several other keys that need to be researched further and possibly included in the USB device analysis process.  I was also able to see that there were a number of event records that pertain to the use of USB devices.

Another example where this sort of analysis can be applied is in determining artifacts corresponding to a CD or DVD being burned on a Windows 7 system.  The System Event Log will have an event record with a source name of "cdrom" and an event ID of 133, indicating that the CDROM was locked for exclusive use.  If the user burned an ISO image, you'll see an indication of the access to the ISO image beneath the user's RecentDocs key, just prior to the ID 133 event.  If the user chose to send a selection of files to the CD/DVD drive and to "burn a disk", you'll likely see an isoburn.exe Prefetch file.

Again, it's very clear that timelines are an extremely valuable technique, not only for analysis of acquired images, but also when conducting research with respect to developing context and an increased relative confidence in the data and events in which you may be interested.

2 comments:

ecophobia said...

Timelines, especially the visual ones tend to add a lot of weight to the findings. Good staff as usual.

Corey Harrell said...

I agree about timelines being very useful technique for conducting research. It makes it easier to see the impact an action has on a system. Plus, it's a great way to practice the technique so you better understand what you are seeing during an examination.