Over the past few months, we’ve published multiple posts here about ransomware – Surprise, Petya/Mischa, Cerber, and cuteRansomware to name a few. One of the common themes that we’ve seen across these different strains of ransomware is cloud apps playing a role in each attack. However, as I looked back on these recent examples, it wasn’t the similarities – the use of cloud apps – that struck me. Rather, it was the different roles that cloud apps were playing in these ransomware attacks. As we all continue to look for ways to bolster our defenses against ransomware and other malware, I thought it might be useful to take a step back and enumerate the ways that we’ve seen cloud apps being used by ransomware today.
To guide this thought process, I used the seven stages from Lockheed Martin’s well-known Cyber Kill Chain® as a framework:
(I won’t go further into the kill chain here. If you’re interested in learning more on how to apply this framework for threat intelligence or to defend against advanced persistent threats, check out this link.)
Delivery | Exploitation | Installation
Starting at the top of the kill chain, there are numerous examples of cloud apps being used to deliver ransomware. Petya and Mischa both used e-mails containing links to cloud storage apps – Dropbox and MagentaCloud respectively – to attempt to deliver the ransomware payload to their victims. Surprise ransomware also used a cloud app to deliver the payload. In this case, however, the attackers were able to find compromised credentials and use TeamViewer – a remote control cloud app used for support – to remotely deliver ransomware to victims’ computers. Furthermore, the attacker was able to easily move through the exploitation and installation stages of the kill chain by using TeamViewer to remotely execute the ransomware package rather than rely on an end user to make a poor decision.
In general, cloud storage and collaboration apps can also be used (intentionally or unintentionally) as a delivery mechanism to secondary targets. As we’ve mentioned in the past, the malware fan-out effect can accelerate the propagation of new malware within an organization by targeting cloud storage sync folders.
Command & Control | Action on Objectives
The more recent example of cuteRansomware added a new wrinkle to how cloud apps can be involved in the ransomware kill chain. cuteRansomware uses Google Docs to collect information about its victims and hold their ransomware encryption keys, in effect making Google Docs a part of the ransomware’s command & control infrastructure.
Finally, looking at the final stage of the kill chain – action on objectives – the malware fan-out effect mentioned above can also amplify the effects of ransomware in an organization by rapidly spreading the unauthorized encryption across an organization. Thinking beyond ransomware, cloud apps are also being used for data exfiltration, which is the ultimate objective of many targeted attacks and insider threats.
Breaking the Chain
The reason for the increased use of cloud apps across many stages of the ransomware kill chain is directly related to the popularity of cloud apps and the rapid growth in usage of both sanctioned and unsanctioned apps in most organizations. This trend also presents a tough challenge to security teams trying to disrupt the use of cloud apps at one or more points in the kill chain. Take the cuteRansomware example above and suppose your organization is using Google Docs as a key productivity tool. In this case, is it feasible to block access to Google Docs to cut off cuteRansomware’s command and control channel? Or in the case of Petya, which attempts to deliver its payload using a Dropbox link, could you block Dropbox completely in your organization to defeat this delivery mechanism?
In both of these cases, a more nuanced approach to controlling cloud apps is needed. Imagine being able to safely enable your organization’s specific instance of Google Docs or Dropbox while restricting the use of those cloud apps in the case of an unknown (or known malicious) instance. Netskope’s ability to deliver granular visibility and control of cloud apps, down to specific apps and app instances, makes this a reality for hundreds of organizations around the world.
