Backdoor.BAT.XERYC.A

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It does not have any propagation routine.

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information. However, as of this writing, the said sites are inaccessible.

Arrival Details

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Backdoor drops the following files:

• %ProgramData%\WinRar.ps1
• %ProgramData%\WinRar.bat

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It adds the following processes:

• %System%\cmd.exe /K {malware fullpath}
• %System%\cmd.exe /S /D /c" echo Y "
• reg add HKCU\Software\Microsoft\Windows\CurrentVersion\Run /v "SecurityHelper" /t REG_SZ /d "\"%ProgramData%\WinRAR.bat\"" /f
• powershell.exe -ExecutionPolicy Bypass -WindowStyle Hidden -NoProfile -File "%ProgramData%\WinRAR.ps1"
• runas -noexit -c whoami /priv
• shutdown /r /t 0
• shutdown /s /t 0

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.. %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It injects itself into the following processes running in the affected system's memory:

• explorer.exe

It adds the following mutexes to ensure that only one of its copies runs at any one time:

• mCm3NbtweBexBwESanCD8TZ5j2UFZ9l9

Autostart Technique

This Backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
SecurityHelper = %ProgramData%\WinRAR.bat

Other System Modifications

This Backdoor modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows Defender\Real-Time Protection
DisableRealtimeMonitoring = 1

Propagation

This Backdoor does not have any propagation routine.

Backdoor Routine

This Backdoor executes the following commands from a remote malicious user:

• List All Available Drives on the System
• List Files and Directories
• File Operations: Create, Delete. Rename, Move, Copy, and Execute Files
• File Upload
• File Download
• Arbitrary Commands

It connects to the following websites to send and receive information:

• {BLOCKED}.{BLOCKED}.138.100:4446

However, as of this writing, the said sites are inaccessible.

Rootkit Capabilities

This Backdoor does not have rootkit capabilities.

Information Theft

This Backdoor gathers the following data:

• OS Version
• Username
• Hostname
• Domain Name
• Keystrokes
• List of Installed Anti-Virus Products
• List of Drives
• Hardware Devices Information
• Login Information
• Total System Uptime

Other Details

This Backdoor does the following:

• It patches the clr.dll to disable AMSI Scanning.
• It steals browser information from the following:
  • Chrome
  • Edge
  • Firefox
  • Brave
• It uses the following configuration to setup AnyDesk in the system:
  • ad.anynet.pwd_hash={BLOCKED}77459d5c108877fd130a161d169ff2f143dffe914dd12bac71364aff65
  • ad.anynet.pwd_salt={BLOCKED}d5ec543ae481906af92eb0f694
• It creates the following directory if AnyDesk is installed in the system:
  • %Application Data%\AnyDesk
• It creates the following files if AnyDesk is installed in the system:
  • %Application Data%\AnyDesk\service.conf → contains AnyDesk configuration
• It gets the value of the following registry entry:
  • HKEY_CURRENT_USER\{domain name}{username}{host name}\Niickname

It does not exploit any vulnerability.