A newly observed Remote Access Trojan (RAT) targeting Windows systems is using Tor2Web proxies for communication with the command and control (C&C) server, Cisco Talos security researchers warn.
The RAT was written in Go, which is rather unusual for Windows malware, and its author refers to it as Athena, which determined the security researchers to call it AthenaGo. The Trojan, Cisco Talos threat researcher Edmund Brumaghin explains, can download and run additional binaries on the infected system, besides relying on Tor2Web proxies for communication purposes.
The malware is distributed via macro-enabled Word documents, an incresingly popular delivery method that was recently used to drop macOS malware as well. The malicious documents distributing AthenaGo appear to be targeting Portuguese speaking users, as the message that instructs potential victims to enable macros was written in Portuguese.
AthenaGo, one of the few Windows malware families to have been written in Go, comes with two hardcoded domains that it connects to post-infection. Both utilize Tor2Web, a project that allows access to resources on the Tor (The Onion Router) network even if the requesting client system isn’t part of the network.
“Tor2Web servers act as proxies and allow clients to access servers hosting content on Tor without requiring the installation of a local Tor client application. This approach has shown to be increasingly attractive to cybercriminals. The use of Tor2Web and Tor in general allows them to stay anonymous. It also makes it much more difficult to remove malicious content being hosted on servers within Tor, as it is difficult to identify where a Tor server is hosted physically,” the security researcher explains.
During the initial infection process, AthenaGo generates public and private RSA keys that are used to communicate with the C&C server, after which it makes two HTTP HEAD requests to the two hardcoded servers.
The malware includes support for various commands that it executes when receiving instructions from the C&C server: ListDir (for a list of directories on the infected system), ListProcesses (generates a list of processes), KillProcess (to execute the taskkill command against a target process), DownloadFile (to download and save a file), DLRUN (to download a file, save it to %TEMP% and execute it), and RunCMD (to execute system commands on the infected system using Go’s os/exec package)
“Malware authors will continue to evolve their attacks as they identify ways to effectively reduce their risk of being caught. This includes relying on C&C infrastructure hosted on Tor, making use of varying levels of encryption to protect the nature and content of network communications with their malware, and limiting their attacks to targeted attacks against specific targets or demographics. AthenaGo is an example of changes in the way malware is being written in an attempt to evade network defenses and successfully compromise target environments,” Cisco Talos’ researcher concludes.