Cloud Threats Memo: Multiple DarkGate Loader Campaigns Exploiting Legitimate Cloud Services

DarkGate Loader is a commodity malware loader with multiple features including the ability to download and execute files to memory, a Hidden Virtual Network Computing (HVNC) module, keylogging, information-stealing capabilities, and privilege escalation. Its distribution mechanism also makes use of legitimate AutoIt files to inject the malicious payload.

The DarkGate Loader is normally distributed via phishing emails delivering malicious VBS or MSI files that install the payload via AutoIt scripts; however between the end of August and October 2023, DarkGate has been deployed in campaigns characterized by the exploitation of several cloud services across the attack chain. For example, in a campaign discovered by researchers at Truesec at the end of August 2023, the distribution mechanism leveraged Microsoft Teams to deliver the malicious payload hosted on a Microsoft SharePoint site. Similarly, in a different campaign discovered by researchers at Trend Micro and active from July to September 2023, the attackers used a different instant messenger (IM) application (Skype) for delivering the link to the malicious payload hosted, once again, on a Microsoft SharePoint site of the same compromised organization.

But the DarkGate campaigns exploiting cloud services don’t end up here. Researchers at WithSecure have recently exposed a new wave of attacks leveraging the same malware to target entities in the U.K., the U.S., and India. This latter campaign has been linked to the same Vietnamese actors associated with the use of the infamous Ducktail stealer, and the attack chain was similar to the previous ones, with the difference that a distinct cloud application was exploited for the initial access (a LinkedIn message) two new cloud services were abused for hosting the malicious payload (Google Drive and Dropbox in different variants of the campaign).

Interestingly, this is not the first time that the threat actors behind Ducktail leverage cloud services to deliver their malicious payload, back in May 2023, researchers from Meta unearthed a long-lasting campaign by the same threat actor using LinkedIn as the initial attack vector, and hosting the malicious payload in file-hosting services such as Dropbox and Mega.

What do these campaigns have in common? A flexible malicious payload, and a flexible cloud infrastructure to deliver it. More than 50% of malware is delivered from the cloud, so it is no surprise that threat actors constantly seek out an increasingly complex attack chain where multiple legitimate services are chained with the sole purpose to lure the victims to download the malicious payload, and to evade the legacy web (and email) security technologies that are not instance-aware, not suited to inspect SSL traffic at scale, and hence blind to the context.

Mitigating the risk of legitimate cloud services exploited for malicious purposes

Microsoft Teams, Microsoft SharePoint, Google Drive, and Dropbox are among the thousands of cloud services where the Netskope Next Gen SWG can provide granular access control, threat protection, and DLP capabilities. They are also among the hundreds for which instance detection is available. So, in cases where these services are exploited to deliver a malicious payload, or to host the command and control infrastructure, it is possible to configure a policy for preventing potentially dangerous activities (such as “Upload” and “Download”) for these services in case they are not needed by the organization, singularly or as a category; or also for preventing these risky activities from non-corporate instances only, in case the apps are in use by the organization.

Netskope customers are also protected against malware distributed from a legitimate cloud service and the web in general by Netskope Threat Protection, which 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 Cloud Exchange provides powerful integration tools to leverage investments across users’ security posture through integration with third-party tools, such as threat intelligence feeds and endpoint detection technologies.

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!