A financially motivated threat actor known as UNC4990 is weaponizing USB devices as an initial infection vector to target organizations in Italy.
Mandiant, owned by Google, said the attacks target several industries, including healthcare, transportation, construction and logistics.
“UNC4990 operations typically involve widespread USB infection followed by deployment of the EMPTYSPACE downloader,” the company said in a report on Tuesday.
“During these operations, the cluster relies on third-party websites such as GitHub, Vimeo, and Ars Technica to host additional coded steps, which it downloads and decodes via PowerShell early in the execution chain.”
UNC4990, active since late 2020, is assessed to operate outside Italy based on extensive use of Italian infrastructure for command and control purposes (C2).
It is currently unknown whether UNC4990 only functions as an initial access facilitator for other actors. The threat actor’s ultimate goal is also unclear, although in one case an open source cryptocurrency miner is said to have been deployed after months of beaconing activity.
Details of the campaign were previously documented by Fortgale and Yoroi in early December 2023, with the former tracking the opponent under the name Nebula Broker.
The infection begins when a victim double-clicks a malicious LNK shortcut file on a removable USB device, leading to the execution of a PowerShell script responsible for downloading EMPTYSPACE (aka BrokerLoader or Vetta Loader) from one remote server via another Intermediate PowerShell script hosted on Vimeo.
Yoroi said he identified four different variants of EMPTYSPACE written in Golang, .NET, Node.js and Python, which subsequently serve as a conduit to retrieve next-stage payloads over HTTP from the C2 server, including a backdoor called QUIETBOARD.
One notable aspect of this phase is the use of popular sites such as Ars Technica, GitHub, GitLab, and Vimeo to host the malicious payload.
“The content hosted on these services presented no direct risk to everyday users of these services, as the content hosted in isolation was completely benign,” Mandiant researchers said. “Anyone who inadvertently clicked or viewed this content in the past was not at risk of being compromised.”
QUIETBOARD, on the other hand, is a Python-based backdoor with a wide range of features that allow it to execute arbitrary commands, alter crypto wallet addresses copied to the clipboard to redirect fund transfers to wallets under their control, propagate malware to removable drives, take screenshots, and collect system information.
Additionally, the backdoor is capable of modular expansion and running independent Python modules such as coin miners, as well as dynamically fetching and executing Python code from the C2 server.
“The analysis of EMPTYSPACE and QUIETBOARD suggests how threat actors have taken a modular approach in developing their toolset,” Mandiant said.
“The use of multiple programming languages to create different versions of the EMPTYSPACE downloader and the change of the URL when the Vimeo video was removed shows a predisposition for experimentation and adaptability on the part of the threat actors.”