As you can see, the challenge is pretty straightforward...an admin found a message "written on their system", and reported it. The questions that Ali posed for the challenge were:
- How was the system hacked?
- What evidence did you find that proved your hypothesis?
- How did you approach and solve the case?
- Anything you would like to add?
Based on what I observed in the data, I would say that the system was not, in fact, hacked. Rather, it appears that the Administrator user logged in from the console, accessed the C:\Tools folder and created the readme.txt file containing the message.
I began with a visual inspection of the image, in order to verify that it could be opened, per SOP. An initial view of the image indicated two user profiles (Administrator, master), and that there was a folder named "C:\Tools". Within that folder was a single file named "readme.txt", which contained the text in question.
From there, I created a timeline of system activity, and started my analysis by locating the file 'C:\Tools\readme.txt' within the timeline, and I then pivoted from there.
The readme.txt file was created on 12 Dec 2015 at approx. 03:24:04 UTC. Approx. 4 seconds later, the Automatic JumpList for Notepad within the Administrator profile was modified; at the same time, UserAssist artifacts indicated that Administrator user launched Notepad.
At the time that the file was created, the Administrator user was logged into the system via the console. Shellbag artifacts for the Administrator account indicated that the account was used to navigate to the 'C:\Tools' folder via Windows Explorer.
Further, there were web browser artifacts indicating that Administrator account was used to view the file at 03:24:09 UTC on 12 Dec 2015, and that the 'master' account was used to view the file at 03:27:23 UTC on the same day.
I created a timeline of system activity from several sources extracted from the image; file system metadata, Windows Event Log metadata, and Registry metadata. In a few instances, I created micro-timelines of specific data sources (i.e., login events from the Security Event Log, activity related to specific users) to use as "overlays" and make analysis easier.
Not related to the analysis goal provided were indications that the Administrator account had been used to access the Desktop\Docs folder for the 'master' user and created the 'readme.txt' file in that folder.
In addition, there was a pretty significant change in the system time, as indicated by the Windows Event Log:
Fri Dec 11 17:30:37 2015 Z
EVTX sensei - [Time change] Microsoft-Windows-Kernel-General/1;
*Time was changed TO 2015-12-11T17:30:37 FROM 2015-12-12T03:30:35
Finally, there was some suspicious activity on 12 Dec, at 03:26:13 UTC, in that magnify.exe was executed, as indicated by the creation and last modification of an application prefetch file. This indicates that this may have been the first and only time that magnify.exe had been executed.
Several seconds before that, it appeared that utilman.exe had been executed, and shortly afterward, net.exe and net1.exe were executed, as well.
Concerned with "Image File Execution Option" or accessibility hijacks, I searched the rest of the timeline, and found an indication that on 11 Dec, at approx. 19:18:54 UTC, cmd.exe had been copied to magnify.exe. This was verified by checking the file version information within magnify.exe. Utilman.exe does not appear to have been modified, nor replaced, and the same appears to be true for osk.exe and sethc.exe.
Checking the Software hive, there do not appear to be any further "Image File Execution Option" hijacks.
I should note that per the timeline, the execution of magnify.exe occurred approx. two minutes after the message file was created.
After I posted this article and Ali commented, I found this blog posted by Adam which also provided a solution to the challenge. Adam had posted his solution on 2 Jan, so last week. I have to say, it's great to see someone else working these challenges and posting their solution. Great job, Adam, and thanks for sharing!
Addendum, 9 Jan:
Based on a whim, I took a look at the USN change journal, and it proved to be pretty fascinating...more so, it showed that following the use of the net.exe/net1.exe, no files were apparently written to the system (i.e., output redirected to a file). Very cool.