Wednesday, December 4, 2013

Daily Blog #164: Solving Sunday Funday 12/1/13 Part 2

Hello Reader,
        Yesterday we left off with a general description on what changed between Windows XP/Vista and 7 as well as versions of Outlook prior to 2007 and their impact on the forensic analysis of attachment access. Today let's go deeper into the artifacts with what is created when attachments are accessed in a Windows 7 system running Outlook 2007.

In this post we will go over whats left in the $MFT, USN Journal and $Logfile when an attachment is accessed and closed before outlook closes. Tomorrow we will focus on what the artifacts look like when the attachment is left open after outlook closes and then finish up this series with conclusions we can draw to answer sundays challenge.

In my test image, which I will provide for you to download tomorrow, I have a Windows 7 system that I have done a couple tests on. I have installed Outlook 2007, Word 2007 and Adobe Reader on this system. I then created a new email account with Yahoo! called and emailed it two different attachments, one pdf version of my cv and one docx version of my cv. I sent two different file types as they create different artifacts from normal access.

When first thinking about this issue you might think that the MRU's for the extensions pdf and docx would be get updated with these files. I have searched the NTUSER.DAT registry for the user minutes after these accesses and within the allocated registry there is no entry made for the opening of these pdf and docx files. Contained within the unallocated space in the registry using yaru from TzWorks I was able to find the following deleted value:
"C:\Users\Suspect\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Outlook\AGI0N64C\cv_cowen_2013.docx"
Left behind by the Microsoft Office Word Previewer when I previewed the message for a second time before opening the attachment directly within Microsoft Word.

So no LNK, no Jumplist, no MRU recent documents key gets created in this access. Within the $MFT I can see only one of the temporary files that was deleted from my first viewing, the other having already been purged out.

This leaves us with the $logfile and USN Journal. The $logfile is helpful here but as the Content.Outlook directory is on a system drive by default it won't last long. So let's look at what the USN Journal knows about my attachment access.

In the 34 seconds that passed between when I opened and closed both attachments we got 18 records from the USN Journal. We can see when each attach was first opened by looking at the file_created flag and we'll have two file_created events for each file as Outlook 2007 by default is extracting two copies of the file on access. I don't know why this is yet and I have seen occasions when it has been only one.

We can see when I closed the file here with the file_deleted, file_closed event. Outlook deletes the file when I close it and this indicator can be a false positive to file deletion. It does represent thought when the open and active file handle closed against the file.

So why does our second file have a (2) after it? For example cv_cowen_2013.pdf and cv_cowen_2013 (2).pdf? The reason is that Outlook never overwrites an existing file and if there are older copies of the attachment that still exist within the 'Content.Outlook' directory the next number in sequence will be used for the newly extracted file.

Interested yet? The USN Journal is an amazing artifact for us in our analysis of Windows Vista and 7 systems, if you are not looking at it, you should be!

Tomorrow lets see what it looks like when I the attachment remains and talk about possible conclusions we can draw.