Backdoor.VBS.ASYNCRAT.B

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 executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

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 adds the following folders:

• %User Temp%\{Random}

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It drops the following files:

• %User Temp%\Good.xml → Uncompiled Loader.
• %User Temp%\{Random}\{Random}.dll → Compiled Loader.
• %User Temp%\{Random}\{Random}.tmp
• %User Temp%\{Random}\{Random}.0.cs
• %User Temp%\{Random}\{Random}.cmdline
• %User Temp%\{Random}\{Random}.out
• %User Temp%\{Random}\{Random}.err
• %User Temp%\{Random}\{Random}.pdb
• %User Temp%\RES{4 Characters}.tmp
• %User Temp%\CSC{4 Characters}.tmp

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It adds the following processes:

• %Windows%\Microsoft.NET\Framework\{version}\MSBuild.exe %User Temp%\Good.xml
• %Windows%\Microsoft.NET\Framework\{version}\csc.exe /noconfig /fullpaths @"%User Temp%\{Random}\{Random}.cmdline"
• %Windows%\Microsoft.NET\Framework\{version}\cvtres.exe /NOLOGO /READONLY /MACHINE:IX86 %User Temp%\RES{4 Characters}.tmp %User Temp%\CSC{4 Characters}.tmp
• %Windows%\Microsoft.NET\Framework\{version}\RegSvcs.exe

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

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

• AsyncMutex_6SI8OkPnk

It injects codes into the following process(es):

• %Windows%\Microsoft.NET\Framework\{version}\RegSvcs.exe

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

Autostart Technique

This Backdoor drops the following file(s) in the Windows Startup folder to enable its automatic execution at every system startup:

• %User Startup%\Startup.vbs → Script to compile Loader.

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, C:\Documents and Settings\{User name}\Start Menu\Programs\Startup on Windows 2003(32-bit), XP and 2000(32-bit), or C:\Users\{user name}\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit), 10(64-bit).)

Other System Modifications

This Backdoor deletes the following folders:

• %User Temp%\{Random} → After use with contents.

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

Backdoor Routine

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

• Ping Test
• Execute Sent Plugin

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

• {BLOCKED}daddy.ddns.net:5946

Information Theft

Upon execution of the affected application, it gathers the following information:

• Hardware ID generated from processor count, username, computer name, OS version, and total size of the system directory
• Username
• Operating System and Architecture
• Current File Path of Malware
• Current Malware Version
• IsAdmin
• Active Window Title
• Installed Antivirus Products
• Installation Time