Ugh

Sorry, I just don't what other title to use...I wasn't able to come up with something witty or pithy, because all I kept thinking was "ugh".

The "ugh" comes from a question (two, actually, that are quite similar) that appear over and over again in the lists and online forums (forii??)...

I have an image of a system that may have been compromised...how do I prove that data was exfiltrated/copied from the system?

Admit it...we've all seen it. Some may have actually asked this question.

Okay, this is the part where, instead of directly answering the question, I tend to approach the answer from the perspective of getting the person who asked the question to reason through the process to the answer themselves. A lot of people really hate this, I know...many simply want to know which button to click in their forensic application that will give them a list of all of the files that had been copied from the system (prior to the image being acquired).

So, my question to you is...with just an image of supposedly victim system, how would you expect to demonstrate that data was copied or exfiltrated from that system?

Well, there are a couple of things I've done in the past. One is to look for indications of collected data, usually in a file. I've seen this in batch files, VBS scripts, and SQL injection commands...commands are run and the output is collected to a file. From there, you may see additional commands in the web server logs that indicate that the file was accessed...be sure to check the web server response code and the bytes sent by the server, if they're recorded.

In other instances, I've found that the user had attached files to web-based email. Some artifacts left after accessing a GMail account indicated that a file was attached to an email and sent to another address. In several instances, this was a resume...an employee was actively looking for a job and interviewing for that position while on company time. Based on file names and sizes (which may or may not be available), used in conjunction with file last accessed times, we've been able to provide indications that files were sent off of the system.

What else? Well, there's P2P applications...you may get lucky, and the user will have installed one that clearly delineates which files are to be shared. Again, this may only be an indication...you may have to access the P2P network itself and see if the file (name, size, hash) is out there.

What about copying? Most analysts are aware of USB devices by now; however, there is still apparently considerable confusion over what indications of the use of such devices reside within an image. One typical scenario is that a user plugs such a device in and copies files to the device...how would you go about proving this? Remember, you only have the image acquired from the system. The short answer is simply that you can't. Yes, you can show when a device was plugged in (with caveats) and you may have file last access times to provide additional indications, but how do you definitively associate the two, and differentiate the file accesses from, say, a search, an AV scan, or other system activity?

I hope that this makes sense. My point is that contrary to what appears to be popular belief, Windows systems do not maintain a list of files copied off of the system, particularly not in the Registry. If your concern is data exfiltration (insider activity, employee takes data, intruder gets on the system and exfils data...), consider the possible scenarios and demonstrate why they would or wouldn't be plausible (i.e., exfil via P2P would not be plausible if no P2P apps are installed). Reason through the analysis process and provide clear explanations and documentation as to what you did, what you found, and justify your findings.