Analysis by: Rhena Inocencio
 Modified by: Mark Joseph Manahan
ALIASES:

Worm.Win32.Vobfus.avrm (Kaspersky), Worm:Win32/Vobfus (Microsoft), W32.Changeup!gen35 (Symantec)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Propagates via removable drives, Dropped by other malware, Downloaded from the Internet

This worm arrives by connecting affected removable drives to a system. 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 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: 30 Jan 2013
Payload: Compromises system security, Connects to URLs/IPs

Arrival Details

This worm arrives by connecting affected removable drives to a system.

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}.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} = "%User Profile%\{random}.exe /{random letter}"

Other System Modifications

This worm adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\WindowsUpdate\
AU
NoAutoUpdate = "1"

It modifies the following registry entries to hide files with Hidden attributes:

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 the following copy(ies) of itself in all removable drives:

  • Passwords.exe
  • Porn.exe
  • {random}.exe
  • Secret.exe
  • Sexy.exe

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:

{garbage characters}
[autorun]
{garbage characters}
IcON={random.exe}
{garbage characters}
open={random}.exe
{garbage characters}
ActIon=22891
{garbage characters}
usEAutoPlAY=1
{garbage characters}

Backdoor Routine

This worm connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}1.{BLOCKED}cks.com
  • {BLOCKED}n.{BLOCKED}2.net
  • {BLOCKED}s.{BLOCKED}1.de
  • {5 digit number}.{BLOCKED}1.de
  • {BLOCKED}i.{BLOCKED}1.de

Download Routine

This worm connects to the following website(s) to download and execute a malicious file:

  • http://{BLOCKED}e.ru/f/mix.exe - detected as TSPY_BANCOS.MAAS
  • http://{BLOCKED}v.ru/l/sc.exe - detected as TSPY_BANCOS.MAAS
  • http://{BLOCKED}v.ru/l/3580c.exe detected as TSPY_BANCOS.MASS

NOTES:

It search for folders in all removable drives then drops copies of itself as {folder name}.exe.

It also uses the filename of the files with the following extensions:

  • .mp3
  • .avi
  • .wma
  • .wmv
  • .wav
  • .mpg
  • .mp4
  • .doc
  • .txt
  • .pdf
  • .xls
  • .jpg
  • .jpe
  • .bmp
  • .gif
  • .tif
  • .png

It then sets the attribute of the original file or folder to Hidden and System to trick users into thinking that the dropped copy is the legitimate file or folder.

It also adds the following non-malicious file in removable drives:

  • x.mpeg

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 9.690.02
FIRST VSAPI PATTERN DATE: 30 Jan 2013
VSAPI OPR PATTERN File: 9.691.00
VSAPI OPR PATTERN Date: 30 Jan 2013

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_VOBFUS.SMMC

    TSPY_BANCOS.MAAS

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete the registry entry with an unknown data 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} = "%User Profile%\{random}.exe /{random letter}"

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_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU
    • NoAutoUpdate = "1"

Step 6

Restore these modified registry values

[ Learn More ]

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: ShowSuperHidden = "0"
      To: ShowSuperHidden = 1

Step 7

Search and delete AUTORUN.INF files created by WORM_VOBFUS.SMMC that contain these strings

[ Learn More ]

{garbage chracters}
[autorun]
icoN={random}.exe,0
{garbage chracters}
open={random}.EXE
{garbage chracters}
actiON=8183
{garbage chracters}
USeAUtopLAY=1
{garbage chracters}

Step 8

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

Step 9

Scan your computer with your Trend Micro product to delete files detected as WORM_VOBFUS.SMMC. 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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