Several state and industrial organizations in Russia fell victim to a custom Go-based backdoor designed for data theft, likely furthering espionage efforts. The campaign was initially detected by Kaspersky in June 2023. Subsequently, in mid-August, Kaspersky identified an updated version of the backdoor characterized by enhanced evasion tactics, signifying the ongoing optimization of the attacks.
The threat actors behind this campaign remain unidentified, and Kaspersky was limited to sharing indicators of compromise that can aid defenders in mitigating these attacks. The assault begins with malicious ARJ archive-laden emails, masquerading as ‘finansovyy_kontrol_2023_180529.rar’ (financial control). This archive contains a ruse PDF document, an NSIS script fetching the primary payload from an external URL (fas-gov-ru[.]com), which is then launched. The malware payload is deposited in ‘C:\ProgramData\Microsoft\DeviceSync’ under the name ‘UsrRunVGA.exe.’
During the same phishing wave, Kaspersky identified two additional backdoors called ‘Netrunner’ and ‘Dmcserv.’ These are essentially the same malware with different command and control server configurations. The backdoor has a variety of functions, including listing files and folders in a specific directory, exfiltrating files to the C2, obtaining clipboard data, capturing desktop screenshots, and searching for specific file extensions to transfer to the C2 server.
To avoid detection from network monitoring solutions, all data transmitted to the C2 is encrypted using AES encryption. To escape analysis, the malware runs checks for usernames, system names, and directories to detect virtualized environments and exits if any are detected. This information is sent to the C2 in the initial phase of infection for victim profiling.
In mid-August, Kaspersky observed a new version of the backdoor with minor alterations, such as the removal of some preliminary checks and the addition of a module for stealing user passwords. This module targets stored passwords in 27 web browsers, including widely used ones such as Chrome, Firefox, Edge, Opera, Brave, Vivaldi, and the trusted Russian browser, Yandex.
Additionally, the malware’s AES key was refreshed in this version, and RSA asymmetric encryption was introduced to secure communications between the client and the command and control server. This campaign underscores the evolving tactics of cybercriminals, including the manipulation of backdoors to steal sensitive data and the use of custom malware to enhance espionage efforts.