Threat Actors Distributing Screenshotter Malware from OneDrive

According to the data collected by Netskope Threat Labs, over the course of 2023, OneDrive was the most exploited cloud app in terms of malware downloads. And if a good day starts in the morning, 2024 does not promise anything good.

In fact, at the beginning of January, and after a nine-month break, researchers from Proofpoint detected a new financially motivated campaign by TA866, a threat actor characterized for being involved in activities related to both cybercrime and cyberespionage.

In their latest campaign, the threat actors flooded targets in North America with several thousands of emails containing PDF documents with subject lines that should entice victims to open the files. PDF files rank steadily on the top of the list of popular malware file types, and this campaign is no exception. The PDFs contained OneDrive URLs that, if clicked, triggered a multi-step infection leading to the installation of the Screenshotter malware payload, a screenshot grabber utility weaponized by the attackers, via a well-known dropper.

In particular, the OneDrive link served a JavaScript file that, if run by the user, would download and run an MSI file, executing the malicious dropper WasabiSeed. The WasabiSeed VBS script would then download and execute a second MSI file containing components of the Screenshotter screenshot utility which would  take a screenshot of the desktop and send it to the C2.

This is yet another example where the attackers leveraged multiple social engineering tricks: a subject teasing the curiosity of the victim, and a legitimate cloud service triggering a sophisticated multi-stage infection chain.

Mitigating the Risks of Malware Delivered from Legitimate Cloud Services

Microsoft OneDrive is one of the thousands of cloud services where the Netskope Next Gen SWG can provide adaptive access control, threat protection, and Data Loss Prevention. It is also one of the hundreds of apps for which instance detection is available. So, in cases where this service, or a similar cloud storage app, is exploited to deliver a malicious payload or to host the command and control infrastructure, whether it is a personal or corporate instance, it is possible to configure a policy for preventing potentially dangerous activities (such as “Upload” and “Download”) if the service is not needed by the organization, singularly or as a category. On the other hand, if the app is in use by the organization, it is possible to configure a policy for preventing any risky activities from non-corporate instances only, mitigating the risk of malware delivery and data exfiltration.

Netskope customers are also protected against malware distributed from a legitimate cloud service and the web in general within sophisticated multi-stage infection chains, by Netskope Threat Protection. 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 detectors for executables and Office documents, and sandboxing with patient zero protection. Netskope threat intelligence can also detect command and control connections even if they are directed to a legitimate cloud service.

Netskope Cloud Exchange provides powerful integration tools to leverage investments across users’ security posture through integration with third-party tools, such as threat intelligence feeds, endpoint protection and email protection technologies (including Proofpoint.)

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

Stay safe!