ESET researchers have discovered a malicious campaign that has been underway since 2016 in four countries of the European Balkan region: Serbia, Croatia, Montenegro, and Bosnia and Herzegovina. The victims of this attack were the financial departments of businesses.
The attackers use malicious emails with links leading to a malicious file as a spreading mechanism. “As the contents of the emails, including links and decoy PDFs, all revolve around taxes, the attackers are apparently targeting accountants in organisations within the region. Therefore, we believe that this campaign is financially motivated,” comments Zuzana Hromcová, the ESET researcher who conducted the investigation.
ESET researchers have uncovered two malicious tools that are instrumental to the campaign. The first tool is a backdoor, the second a remote access Trojan. ESET has named these tools BalkanDoor and BalkanRAT, respectively. “A typical victim of this campaign ends up having both these tools deployed on their computer, each of them capable of fully controlling the affected machine,” says Hromcová.
This rather uncommon “two-tool” setup makes it possible for attackers to choose the most suitable method of controlling the affected computers. “BalkanRAT enables the attackers to remotely control the compromised computer manually, via a graphical interface. BalkanDoor enables them to remotely control the compromised computer via a command line, possibly en masse,” explains Hromcová.
ESET’s analysis of these malicious tools unveiled a number of notable features.
BalkanDoor, an otherwise simple backdoor, is capable of password-less screen-unlocking, which is useful to the attackers in cases when a logged-in user locks their computer. Most recent samples of BalkanDoor exploit a WinRAR ACE vulnerability, which allows the malware to be executed and installed even without the user executing any file.
BalkanRAT, on the other hand, misuses a legitimate commercial remote desktop software that can monitor the victim’s activity and manually control the computer. It also uses extra tools and scripts to hide its presence from the victim, such as hiding the window, the tray icon, and its processes. Both BalkanDoor and BalkanRAT come digitally signed. “We have seen various certificates; one of them was even valid at the time of writing and has been revoked upon our notice,” concludes Hromcová.
ESET security products detect these threats as Win{32,64}/BalkanRAT and Win32/BalkanDoor.
Edited by Fundisiwe Maseko
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