Cloud Threats Memo: Exploiting Legitimate Cloud Services for Command and Control

Welcome to the first edition in 2022 of our Cloud Threats Memo!

One of the key findings of our Cloud and Threat Report – January 2022 is the leadership of Google Drive as the most exploited cloud app for the distribution of malware (and for the record, guess which service ranks at number two—spoiler alert: it is a cloud storage service from Microsoft). Unsurprisingly, this is not the only way in which threat actors can exploit these and other cloud services. Abusing a legitimate cloud service for their command and control infrastructure is another common scenario that generic criminals and state-sponsored actors continue to leverage (for example in a recent campaign an APT group dubbed ITG17, AKA MuddyWater, targeted an Asian airline between 2019 and 2021 via a new backdoor named “Aclop” using Slack as its command and control server, a modus operandi that we know very well, and that we have also exposed via a proof-of-concept exclusively for research purposes.)

To add more resiliency to their malicious infrastructure, threat actors may also leverage a legitimate cloud service as a relay for the real command and control (C2): YouTube is an example of a cloud app frequently exploited, where channel descriptions are used to hide the URLs for malicious attackers’ command and control infrastructure. 

A similar, creative, modus operandi is also being adopted with Google Drive, as reported by researchers from Intezer who, in December 2021, discovered a new backdoor dubbed SysJoker targeting Windows, Mac, and Linux, and is characterized by the ability to generate its command and control by decoding a string retrieved from a text file hosted on Google Drive. This is another example of the way that threat actors can weaponize the flexibility of legitimate cloud services.  A cloud service provides a ready-to-use infrastructure that does not need any additional (error-prone) operations such as the registration of a domain and the allocation of an IP space that can be easily moved to another instance in case the original one is taken over.

How Netskope mitigates the threat of legitimate cloud services exploited for the command and control infrastructure

Google Drive is one of the thousands of services where the Netskope Next Gen SWG can provide granular access control, and one of the dozens for which instance detection is also available. To defend against attacks where a legitimate cloud service is exploited to host malicious command and control infrastructure, it is possible to configure a policy that prevents potentially dangerous activities (such as upload and download) in non-corporate instances. It is possible to make the scope of the policy broader, blocking these activities for any unneeded cloud storage service that can potentially be exploited as a command and control, as a relay (hosting the command and control descriptors), or even to distribute malware.

Needless to say that if a legitimate cloud service is exploited to deliver malware, Netskope customers are also protected by Netskope Threat Protection, which has recently achieved the 2021 On-Demand Malware Detection certification from SE Labs with 100% threat detection on both known malware samples and unknown malware samples and 0% false-positive rate. Netskope Threat Protection scans web and cloud traffic to detect known and unknown threats with a comprehensive set of engines including signature-based AV, machine learning-based detectors, and sandboxing.

Finally, Netskope Advanced Analytics provides specific dashboards to assess the risk of rogue cloud instances being exploited to deliver malware or becoming the target of anomalous communications, with rich details and insights, supporting security teams in the analysis and remediation process.

Stay safe!