ALIASES:

W32/Vasor.b (McAfee); W32.Vasor (Symantec); Worm.Win32.Vasor.17400 (Kaspersky); BehavesLike.Win32.Malware.bsf (vs) (Sunbelt); Worm/Vasor (AVG)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 REPORTED INFECTION:

  • 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.

  TECHNICAL DETAILS

File Size: 220,160 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 05 Jul 2013

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%\RECYCLER\S-1-5-21-3623455640-1605238121-007859134-6157\MsMxEng.exe

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It creates the following folders:

  • %User Temp%\Task
  • %System Root%\RECYCLER
  • %System Root%\RECYCLER\S-1-5-21-3623455640-1605238121-007859134-6157

(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.. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Taskman = "%System Root%\RECYCLER\S-1-5-21-3623455640-1605238121-007859134-6157\MsMxEng.exe"

Other System Modifications

This file infector adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%User Temp%\svchost.exe = "%User Temp%\svchost.exe:*:Enabled:Krosavcheg"

Dropping Routine

This file infector drops the following files:

  • %User Temp%\svchost.exe
  • %System Root%\RECYCLER\S-1-5-21-3623455640-1605238121-007859134-6157\Desktop.ini

(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.. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine: 9.300

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

Identify and delete files detected as PE_VASOR.A using either the Startup Disk or Recovery Console

[ Learn More ]

Step 3

Delete this registry value

[ Learn More ]

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Taskman = "%System Root%\RECYCLER\S-1-5-21-3623455640-1605238121-007859134-6157\MsMxEng.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %User Temp%\svchost.exe = "%User Temp%\svchost.exe:*:Enabled:Krosavcheg"

Step 4

Search and delete these components

[ Learn More ]
There may be some components that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %User Temp%\svchost.exe
  • %System Root%\RECYCLER\S-1-5-21-3623455640-1605238121-007859134-6157\Desktop.ini

Step 5

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %User Temp%\Task
  • %System Root%\RECYCLER
  • %System Root%\RECYCLER\S-1-5-21-3623455640-1605238121-007859134-6157

Step 6

Scan your computer with your Trend Micro product to clean files detected as PE_VASOR.A. 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.


Did this description help? Tell us how we did.