WORM_VB.SMRX

August 23, 2014
 Analysis by: kathleenno
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This malware drops .LNK files in removable and mapped drives that point to a copy of itself. This is done to automatically execute dropped copies when the said drives are accessed. These .LNK files use the certain file names:

It also uses the names of existing folders. This routine enables the copy of the worm to execute first before opening the real folder or file. It then changes the attributes of the original folders and files to Hidden and System to avoid early detection.

It also adds the certain files in the said drives

This worm arrives via removable drives. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It drops copies of itself in all removable drives. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size:

Varies

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

07 Jan 2011

Arrival Details

This worm arrives via removable drives.

It may arrive via network shares.

It 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 worm drops the following copies of itself into the affected system:

  • %User Profile%\{random filename}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random filename} = "%User Profile%\{random file name}.exe"

Other System Modifications

This worm modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = "0"

(Note: The default value data of the said registry entry is 1.)

Propagation

This worm drops copies of itself in all removable drives.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[AuTORUn]
action=Open folder to view files
SHelleXeCUte={random filename}.eXE
icon=%sysTEmrOOT%\SYSTem32\SHeLl32.Dll,4
usEAUToplAY=1

NOTES:

This malware drops .LNK files in removable and mapped drives that point to a copy of itself. This is done to automatically execute dropped copies when the said drives are accessed. These .LNK files use the following file names:

  • Documents.lnk
  • Music.lnk
  • New Folder.lnk
  • Passwords.lnk
  • Pictures.lnk
  • Video.lnk

It also uses the names of existing folders. This routine enables the copy of the worm to execute first before opening the real folder or file. It then changes the attributes of the original folders and files to Hidden and System to avoid early detection.

It also adds the following files in the said drives:

  • ert.dll - detected as TROJ_ZAPCHAST.LA
  • {random file name}.lnk - detected as EXPL_CPLNK.SM

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

7.752.12

FIRST VSAPI PATTERN DATE:

07 Jan 2011

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

Remove the malware/grayware file dropped/downloaded by WORM_VB.SMRX. (Note: Please skip this step if the threat(s) listed below have already been removed.)

    EXPL_CPLNK.SM
    TROJ_ZAPCHAST.LA

Step 3

Scan your computer with your Trend Micro product and note files detected as WORM_VB.SMRX

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random filename} = %User Profile%\{random filename}.exe

Step 6

Restore this modified 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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: ShowSuperHidden = 0
      To: 1

Step 7

Search and delete AUTORUN.INF files created by WORM_VB.SMRX that contain these strings

[ Learn More ]
[AuTORUn]
action=Open folder to view files
SHelleXeCUte={random filename}.eXE
icon=%sysTEmrOOT%\SYSTem32\SHeLl32.Dll,4
usEAUToplAY=1

Step 8

Search and delete this file

[ Learn More ]
There may be some files 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.
  • Documents.lnk
  • Music.lnk
  • New Folder.lnk
  • Passwords.lnk
  • Pictures.lnk
  • Video.lnk

Step 9

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_VB.SMRX. 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.