Backdoor.VBS.ASYNCRAT.B
HEUR:Trojan.VBS.Alien.gen (KASPERSKY)
Windows
Threat Type: Backdoor
Destructiveness: No
Encrypted: Yes
In the wild: Yes
OVERVIEW
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.
TECHNICAL DETAILS
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
SOLUTION
Step 1
Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.
Step 2
Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.
Step 3
Restart in Safe Mode
Step 4
Search and delete this file
- %User Temp%\RES{4 Characters}.tmp
- %User Temp%\CSC{4 Characters}.tmp
- %User Temp%\Good.xml
- %User Startup%\Startup.vbs
Step 5
Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.VBS.ASYNCRAT.B. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.
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