Analysis by: jasperm
ALIASES:

Microsoft: Worm:Win32/Slenfbot.AKD ; Kaspersky: IM-Worm.Win32.Yahos.mb

 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 instant messaging applications

This worm sends messages that contain links to sites hosting remote copies of itself using the instant-messaging (IM) applications Yahoo Messenger and MSN Messenger.

It may also send messages containing malicious links using Facebook chat feature.

It opens an Internet Explorer window and connects to a website.

This worm may be dropped by other malware. It may be unknowingly downloaded by a user while visiting malicious websites.

It modifies certain registry entries to disable the Automatic Windows Update feature. This action prevents the affected system to be notified when critical Windows updates are available.

It connects to a website to send and receive information.

  TECHNICAL DETAILS

File Size: 94,208 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 27 Jan 2011
Payload: Compromises system security, Terminates processes

Arrival Details

This worm may be dropped by other malware.

It may be unknowingly downloaded by a user while visiting malicious websites.

Installation

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

  • %Windows%\nvsvc32.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
NVIDIA driver monitor = %Windows%\nvsvc32.exe

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
NVIDIA driver monitor = %Windows%\nvsvc32.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Terminal Server\
Install\Software\Microsoft\
Windows\CurrentVersion\Run
NVIDIA driver monitor = %Windows%\nvsvc32.exe

Other System Modifications

This worm modifies the following registry entries to disable the Active Windows Update feature:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wuauserv
Start = 4

(Note: The default value data of the said registry entry is 2.)

Propagation

This worm sends messages that contain links to sites hosting remote copies of itself using the following instant-messaging (IM) applications:

  • Yahoo Messenger
  • MSN Messenger

Backdoor Routine

This worm connects to the following websites to send and receive information:

  • {BLOCKED}oshistory.info
  • {BLOCKED}i.albertoshistory.info
  • {BLOCKED}emccloskey.org
  • {BLOCKED}rlounge.de
  • {BLOCKED}p.phoenix-cc.net
  • {BLOCKED}ger.x-y.net
  • {BLOCKED}lofaccountancy.com
  • {BLOCKED}ls.lww.com
  • {BLOCKED}s.archivum.info
  • {BLOCKED}s.josbank.com
  • {BLOCKED}s.juegosbakugan.net
  • {BLOCKED}s.mtime.com
  • {BLOCKED}s.tguia.cl
  • {BLOCKED}p.lvengine.com
  • {BLOCKED}astpost.org
  • {BLOCKED}x.price-erotske.in.rs
  • {BLOCKED}d.longjuyt2tugas.com
  • {BLOCKED}e.oaklandathletics.com
  • {BLOCKED}n.51.com
  • {BLOCKED}service.com
  • {BLOCKED}idyscrubs.com
  • {BLOCKED}yle.com
  • {BLOCKED}mpton.ac.uk
  • {BLOCKED}r-uni-sw.eesp.ch
  • {BLOCKED}dvisor.com
  • {BLOCKED}s.linkedin.com
  • {BLOCKED}ed.com
  • {BLOCKED}ek.com
  • {BLOCKED}etrafficspy.com
  • xxx.{BLOCKED}m.de
  • xxx.{BLOCKED}atka.pl

Process Termination

This worm terminates the following processes if found running in the affected system's memory:

  • msseces.exe

Other Details

This worm does the following:

  • It may also send messages containing malicious links using Facebook chat feature.
  • It opens an Internet Explorer window and connects to http://{BLOCKED}users.myspace.com/Browse/Browse.aspx.

  SOLUTION

Minimum Scan Engine: 8.900
VSAPI PATTERN File: 7.796.14
VSAPI PATTERN Date: 27 Jan 2011
VSAPI PATTERN Date: 1/27/2011 12:00:00 AM

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Identify and terminate files detected as WORM_YAHOS.AL

[ Learn More ]
  1. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  2. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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\CurrentVersion\Run
    • NVIDIA driver monitor = %Windows%\nvsvc32.exe
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • NVIDIA driver monitor = %Windows%\nvsvc32.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Terminal Server\Install\Software\Microsoft\Windows\CurrentVersion\Run
    • NVIDIA driver monitor = %Windows%\nvsvc32.exe

Step 4

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wuauserv
    • From: Start = 4
      To: Start = 2

Step 5

Scan your computer with your Trend Micro product to delete files detected as WORM_YAHOS.AL. 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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