The example involves a user who tried to download an unauthorized version of TeamViewer (an app that has actually been used as camouflage for trojan spyware before).
The user downloaded a malicious file disguised as a crack installer for the application.
After downloading and executing these files, one of the child processes created other files and the executable setup.exe/setup-installv1.3.exe, which was extracted from 320yea_Teamviewer_15206.zip via WinRAR.exe. This file seems to be the source of most of the downloaded malicious files.
Afterward, the file aae15d524bc2.exe was dropped and executed via Command Prompt. It then spawned a file, C:Users{username}DocumentsetiKyTN_F_nmvAb2DF0BYeIk.exe, which sequentially initiated the BITS admin download.
BITS admin is a command-line tool that can help monitor progress and create, download, and upload jobs. The tool also allows a user to obtain arbitrary files from the internet, a feature that attackers can abuse.
Analysts also observed that information in the browser’s credential store was taken by the attacker.
Specifically, the stored data in C:Users{username}AppDataLocalMicrosoftEdgeUser DataDefaultLogin was copied. Credentials stored in browsers are often critical personal data that could be leveraged by attackers to gain access into personal, business, or financial accounts. Attackers can even compile and sell this information in underground markets.
To maintain persistence, an executable file was entered in the AutoStart registry and a scheduled task was created:
Create scheduled task: C:WindowsSystem32schtasks.exe /create /f/sc onlogon /rl highest /tn”services64″/tr ‘”C:Users{username}AppDataRoamingservices64.exe”‘
AutoStart registry: HKCUSOFTWAREMicrosoftWindowsCurrentVersionRunprun:C:WINDOWSPublicGamingprun.exe
As previously mentioned, these cases come about because users search for free applications and trust that someone is going to put the cracked or stolen full version online as a gesture of good will. But, attackers simply take advantage of those who download these files.
Following the execution of setup_x86_x64_install.exe, it created and executed a new file named setup_installer.exe that dropped several files and queried several domains.