Archives For Computer Forensics

It wasn’t that long ago that every report I read containing Windows prefetch artifacts included only the basics: executable name, first and last time executed (now eight timestamps in Win8), and number of executions. There is much more information stored in prefetch files, but until recently there were few tools to easily parse and provide it to the examiner. Mark McKinnon wrote one of the first prefetch parsers to include full path names for additional files accessed within the first ten seconds of application launch. TZWorks’ pf tool now also provides this information. Depending on case type, this information could be overkill, but imagine a prefetch file tracking execution of a malicious binary while also identifying a related malicious DLL loaded, or the location of keylog output. A lot of files are accessed within the first ten seconds of execution, so you may find evidence of specific documents opened in the prefetch file for the Microsoft WinWord application or in the case of Figure 1, files accessed within zip archives via a 7zip prefetch file.


Figure 1: Excerpt showing file access recorded inside a prefetch file (output from TZWorks pf)

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One of the great pleasures of performing Windows forensics is there is no shortage of application execution artifacts.  Application execution tells us what has run on a system and is often the pivot point that reveals important activity on the system.  Why was FTP run on this workstation?  Is it normal to see execution of Winsvchost.exe?  Why was a privacy cleaning tool used for the first time during the system owner’s last week of work?  While undoubtedly useful, our adversaries are more forensic-aware than ever and often take steps to eliminate application execution artifacts.  At CrowdStrike we routinely encounter nation-state groups that attempt to delete Prefetch.  Even the popular CCleaner anti-forensics tool defaults to clearing Prefetch and UserAssist data.  Hence having additional sources of data can often mean the difference between an easy examination and a long, painful one.CCleaner Prefetch Delete

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It has been over six months since Edward Snowden’s unprecedented NSA leaks, and we are still a long way from being able to assess the damage. Worldwide trust in United States tech companies has undoubtedly been shaken. Cisco Systems blamed a ten percent revenue drop on fallout from the leaks. Microsoft is offering the ability for foreign customers to have their data stored outside of the United States. And Silicon Valley stalwarts from Apple to Google to Yahoo have spent considerable resources defending themselves as each new embarrassing revelation becomes public. The trickle-down effect of this is even touching the small niche of digital forensics. Personal privacy has been central to the Snowden debate, and users today are more educated than ever about how their information is stored and transmitted. Web services companies are taking notice, and we have already seen some very useful artifacts disappear. I expect the trend to continue and would like to share a few examples.

Google Chrome

On October 1, 2013, version 30 of Google Chrome was released. Absent in this release was one of the most unique browser artifacts available: History Index files. Prior to version 30, Chrome not only stored browser history, cache and cookies but also recorded a full text index of each visited page. Since page content can change, this was a wonderful forensic artifact for proving what existed on a given page when a user viewed it. Chrome version 30 not only stopped recording this information, it also deleted any existing History Index files from the user’s profile.

Google Chrome Index c2body

Figure 1: The Chrome c2body field previously held a full text index of visited pages.

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Oct 16


The Forensics From the Sausage Factory blog details a different technique for EXIF data carving here.

Oct 7

SANS recently posted a webcast I recorded on memory forensics.  While the presentation is from early 2012, the concepts are solid and this deck was eventually expanded to the full day of memory forensics training present in the updated Forensics 508 course.

Jun 11

The GUI control panel is a long-standing feature of Microsoft Windows, facilitating granular changes to a vast collection of system features.  It can be disabled via Group Policy but is largely available to most user accounts (administrative permissions are required for some changes).  From a forensic perspective, we can audit control panel usage to identify a wide range of user activity:

  • Firewall changes made for unauthorized software (firewall.cpl)
  • User account additions / modifications (nusrmgr.cpl)
  • Turning off System Restore / Volume Shadow Copies (sysdm.cpl)
  • System time changes (timedate.cpl)
  • Interaction with third-party security software applets

While identifying individual system modifications is difficult, at a minimum we can show that a user accessed a specific control panel applet at a specific time.  Context provided by other artifacts may provide further information.  As an example, imagine you were reviewing control panel usage on a system and came across Figure 1.

Brutus Password Cracker

Figure 1: Sample Userassist Output

Context is critical, and, while access to the Windows Security Center might not normally be particularly interesting, the fact that it was accessed immediately following the execution of a known (router) password cracking tool might make all the difference.

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With the major expansion of forensic curriculum at the SANS Institute, I frequently get questions about what class(es) to take. If you are trying to decide between FOR408 (Windows Forensics) and FOR508 (Advanced Forensics and Incident Response), this is the best comparison I have seen online.

I found the following quote particularly insightful: “508 is not a more advanced version of the 408, it’s a completely different course with completely different objectives.”

Last year I covered the free Encrypted Disk Detector (EDD) tool and challenged the community to help crowdsource its development [link].   Thank you to all that took part in the experiment.  Magnet Forensics announced today that Encrypted Disk Detector version 2 is available [get it here].

Survey Results

In addition to encouraging additional development of EDD, a side benefit of the project was to get an idea of the most popular disk encryption products being deployed.  Figure 1 provides the survey results, with Checkpoint Full Disk Encryption, Symantec Endpoint Encryption, and Sophos (formerly Utimaco) Safeguard rounding out the top three.   I think many of us could have guessed that big players like Symantec and Sophos would be near the top, but I was surprised to see products like BestCrypt and SecureDoc pull ahead of Credant Technologies (now owned by Dell).

EDD Survey Results

Figure 1: EDD Survey Results

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