Performing malware analysis during incident response can be an exciting, creative exercise. But it can also be a nebulous process, with no clear beginning and no defined end state. While there are numerous articles, books, and tools that cover the topic, the sheer volume of resources can sometimes lead to decision fatigue, and the question becomes: What do I do next? To focus your attention and guide your analysis, begin by answering the four key questions set forth below.
To be clear, my intent is not to create a comprehensive list of questions, but to highlight the ones that will yield the most value. If you work on answering these questions first, you will stay on task, make real progress, and better understand the next few steps in the context of your specific incident.
1) What are the artifacts of execution?
This question will fuel your static and behavioral analysis of the sample. Your precise goal is to document activity on the file system, in memory, and across the network. This includes launched processes, created and deleted files, modified registry entries, and command and control network traffic. Assume the malware sample has the highest level of privilege on your network and has access to all the local and online resources it needs. Also, consider interacting with your analysis environment by launching enterprise applications, browsing to common sites, and rebooting the machine to facilitate activity. Be sure to record any active you observe.
2) What is the potential impact of code execution?
This question expands upon the first question by requiring you to dig deeper and piece together observed activity to determine functionality and purpose. For example, perhaps you observed a file created during behavioral analysis. You must now determine what this file is used for. Does it log keystrokes? Perhaps it stores encoded configuration data that the malware relies upon. Answering this question often requires iterative testing (an important reason to use virtual machines and create snapshots throughout analysis). Reaching a solution may be as simple as completing a few Google searches or may involve more complex code analysis.
3) What is the potential impact of code execution in your environment?
Notice the difference between this question and the second question. While understanding the absolute potential impact is important, in the context of an enterprise security incident, your management is most concerned about the impact on the corporate network. Becoming equipped with the answer to this question and differentiating it from the previous one is a distinguishing factor between a shining, proficient malware analyst and a reckless one.
4) What are the sample’s key host and network indicators of compromise (IOCs)?
Review your artifacts of execution, including registry keys, file names and locations, hashes, C&C specifics, and strings to highlight key information which will allow you to seek out similar activity across the network. This information will not only expedite the detection of other compromised machines on the network, but it will also feed into generating valuable threat intel for your organization and any information sharing partners.
As you try to answer these questions, remember that malware analysis is an iterative process. You may not answer each question in totality with 100% certainty before moving onto the next. This is why performing malware analysis is similar to the practice of an art – not because it is indescribable or intangible (these are usually symptoms of a poor process); but because it requires patience and the discipline to know what approaches are working, which ones are not, when you need to start over, and when you need to step away and refocus on the problem at another time.
Clearly, there are other important questions to answer, but investigating the ones listed above will get you moving in the right direction, and answering them as quickly as possible will arm you with the information management often needs once an incident kicks off.
Anuj Soni is a Senior Incident Responder at Booz Allen Hamilton, where he leads intrusion investigations and performs forensic and malware analysis to investigate security incidents. He also teaches FOR610: Reverse-Engineering Malware for the SANS Institute. Anuj excels not only in delivering rigorous technical analysis, but also in process development, knowledge management, and team leadership to accelerate incident response efforts. Anuj presents at events including the U.S. Cyber Crime Conference, SANS DFIR Summit, and the Computer and Enterprise Investigations Conference (CEIC). He received his Bachelors and Masters degrees from Carnegie Mellon University.