Cloud Threats Memo: Lampion Exploiting WeTransfer to Deliver Malware

Lampion is a banking trojan with a particular predisposition to targeting Portuguese-speaking users (and exploiting cloud services). First documented in December 2019, the malware has gone through multiple releases, characterized by a number of different mechanisms to deliver the initial VBS (Visual Basic Script Loader).

All the different variants have an element in common, the malware is distributed abusing legitimate cloud services throughout different stages of the attack chain. However, the attackers have constantly changed the apps exploited to deliver the final payload and the latest version, discovered recently by researchers at Cofense, is no exception.

In an attempt to make the delivery process more trusted for the user, simplifying the operational tasks at the infrastructure level, the attackers have been leveraging the popular file-transfer platform WeTransfer. The initial email, spoofing a legitimate company, purports to deliver a proof of payment (a common bait) that should be downloaded from WeTransfer. WeTransfer is of course a familiar and well-known app that many people use for their daily tasks (without too many concerns about the possible security implications). Interestingly the next stage payload is downloaded from AWS, and while using multiple services to distribute their payloads is an established modus operandi for the Lampion threat actor, one of them is always AWS S3.

For the record this is not the first time that WeTransfer has been abused to deliver malware. In a previous campaign it was used to deliver malicious URLs, bypassing Email Security Gateways (there is no limit to the creativity of the attackers), while more recently it has been detected in a campaign distributing the ZLoader malware (in a dangerous mix of cloud services using Google Docs and Box).

Mitigating the risk of file-transfer services exploited to deliver malware

WeTransfer and AWS S3 are among thousands of cloud services for which the Netskope Next Gen SWG provides granular access control through the Cloud XD engine; recognizing dozens of activities such as “Login,” “Create,” “Download,” etc. In the case of AWS S3, it is also possible to distinguish different instances and also create a perimeter of corporate buckets, enforcing different policies. And so it is possible to prevent potentially dangerous activities (such as upload and download) from non-corporate file-transfer services (such as WeTransfer) but also from AWS S3 instances or buckets outside the corporate perimeter. 

And if a managed cloud service is exploited to deliver malware, this risk can be mitigated thanks to Netskope Threat Protection, part of the NG-SWG. This provides an effective defense against modern evasive threats regardless of the nature of the traffic (web or cloud) with a layered approach that offers multiple engines – ranging from antivirus to cloud sandboxing – plus additional detectors based on machine learning to detect Office documents containing malicious macros and portable executables. If needed, the capabilities of the threat protection engine can be further enhanced, integrating external technologies (such as threat intelligence feeds or endpoint technologies), via Cloud Exchange.

Stay safe!