Backdoor.VBS.ASYNCRAT.C

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 drops the following files:

• %User Temp%\Good.xml -> Uncompiled Loader
• %User Temp%\{Random Characters}.tmp -> deleted afterwards
• %User Temp%\{Random Characters}.0.cs -> deleted afterwards
• %User Temp%\{Random Characters}.dll -> serves as a Loader. It is deleted afterwards
• %User Temp%\{Random Characters}.cmdline -> deleted afterwards
• %User Temp%\{Random Characters}.out -> deleted afterwards
• %User Temp%\{Random Characters}.err -> deleted afterwards
• %User Temp%\{Random Characters}.pdb -> deleted afterwards
• %User Temp%\CSC{4 Random Characters}.tmp -> deleted afterwards
• %User Temp%\RES{4 Random Characters}.tmp -> deleted afterwards

(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 Characters}.cmdline"
• %Windows%\Microsoft.NET\Framework\{Version}\cvtres.exe /NOLOGO /READONLY /MACHINE:IX86 "/OUT:%User Temp%\RES{4 Random Characters}.tmp" "%User Temp%\CSC{4 Random Characters}.tmp"
• "%Windows%\Microsoft.NET\Framework\{Version}\RegAsm.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}\RegAsm.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 User Startup folder to enable its automatic execution at every system startup:

• %User Startup%\StartupChrome64.vbs

(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).)

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}a.ddns.net:9582

Information Theft

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

• Active window title
• Current file path of the malware
• Current malware version running in the machine
• Flag stating if the malware is run as admin
• HWID generated from processor count, username, computer name, OS version, and total size of the system directory
• Installed AV products
• OS information
• Time installed
• Username