PE_VASOR.B
Virus:Win32/Vasor.A (Microsoft); W32/Vasor.a (McAfee); W32.Vasor (Symantec); Worm.Win32.Vasor.17400 (Kaspersky); BehavesLike.Win32.Malware.bsf (vs) (Sunbelt); Worm/VB.BNZ (AVG)
Windows 2000, Windows XP, Windows Server 2003
Threat Type: File infector
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This file infector arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It disables Task Manager, Registry Editor, and Folder Options.
TECHNICAL DETAILS
Arrival Details
This file infector 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 file infector drops the following copies of itself into the affected system:
- %System Root%\{malware file name}\{malware file name}.exe
- %System Root%\AUTOEXEC.BAT\AUTOEXEC.BAT.exe
- %System Root%\CONFIG.SYS\CONFIG.SYS.exe
- %System Root%\Documents and Settings\Documents and Settings.exe
- %System Root%\Program Files\Program Files.exe
- %System Root%\WINDOWS\WINDOWS.exe
- {malware path and file name}\{malware file name}.exe
- %System Root%\AUTOEXEC.BAT\AUTOEXEC.BAT.exe
- %System Root%\CONFIG.SYS\CONFIG.SYS.exe
- %System Root%\Documents and Settings\Documents and Settings.exe
- %Program Files%\Program Files.exe
- %Windows%\WINDOWS.exe
- %Windows%\Cursors\services.exe
(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000, Server 2003, and XP (32-bit), Vista (32-bit), and 7 (32-bit), or C:\Program Files (x86) in Windows XP (64-bit), Vista (64-bit), and 7 (64-bit).. %Windows% is the Windows folder, which is usually C:\Windows.)
It creates the following folders:
- %User Temp%\Task
(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, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)
Autostart Technique
This file infector adds the following registry entries to enable its automatic execution at every system startup:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Service = "%Windows%\Cursors\services.exe"
Other System Modifications
This file infector adds the following registry entries:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = "0"
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%User Temp%\svchost.exe = "%User Temp%\svchost.exe:*:Enabled:Krosavcheg"
It modifies the following registry entries:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "0"
(Note: The default value data of the said registry entry is 2.)
It creates the following registry entry(ies) to disable Task Manager, Registry Tools and Folder Options:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer
NoFolderOptions = "1"
Dropping Routine
This file infector drops the following files:
- %User Temp%\svchost.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, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)
This report is generated via an automated analysis system.
SOLUTION
Step 1
Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.
Step 2
Restart in Safe Mode
Step 3
Enable Registry Editor, Task Manager, and Folder options
Step 4
Delete this registry value
Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- Service = "%Windows%\Cursors\services.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- ShowSuperHidden = "0"
- In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
- %User Temp%\svchost.exe = "%User Temp%\svchost.exe:*:Enabled:Krosavcheg"
Step 5
Restore these modified registry values
Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: Hidden = "0"
To: Hidden = ""2""
- From: Hidden = "0"
Step 6
Search and delete this file
- %User Temp%\svchost.exe
Step 7
Search and delete this folder
- %User Temp%\Task
Step 8
Restart in normal mode and scan your computer with your Trend Micro product for files detected as PE_VASOR.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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