WORM_YAHLOVER.RW

 Analysis by: Roland Marco Dela Paz

 ALIASES:

Worm:AutoIt/YahLover.F (Microsoft); :W32/Yahlover.worm.gen.c (McAfee); W32.Imaut.E (Symantec); IM-Worm.Win32.Sohanad.gen (Kaspersky); IM-Worm.Win32.Sohanad.gen (Sunbelt); Win32.Worm.YahLover.C (FSecure)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This worm 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

File Size:

666,667 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

07 Mar 2012

Arrival Details

This worm 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:

  • %System%\chrome.exe
  • %Windows%\chrome.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.. %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_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Yahoo Messengger = "%System%\chrome.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "Explorer.exe chrome.exe"

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

Other System Modifications

This worm adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System

HKEY_LOCAL_MACHINE\Software\Policies\
Microsoft\Internet Explorer\Control Panel

HKEY_CURRENT_USER\Software\Policies\
Microsoft\Internet Explorer\Control Panel

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\Schedule
AtTaskMaxHours = "0"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Default_Page_URL = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"

(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Default_Search_URL = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"

(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd=ie&ar=iesearch.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Search Page = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"

(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd=ie&ar=iesearch.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Start Page = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"

(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd={SUB_PRD}&clcid={SUB_CLSID}&pver={SUB_PVER}&ar=home.)

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
Start Page = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"

(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome.)

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"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = "1"

Other Details

This worm connects to the following possibly malicious URL:

  • http://www.{BLOCKED}m.info/setting.ini
  • http://www.{BLOCKED}m.info/poojasharma2/setting.ini
  • http://www.{BLOCKED}m.info/poojasharma3/setting.ini
  • http://www.{BLOCKED}m.info/poojasharma4/setting.ini

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.200

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 delete files detected as WORM_YAHLOVER.RW using either the Startup Disk or Recovery Console

[ Learn More ]

Step 3

Enable Registry Editor, Task Manager, and Folder options

[ Learn More ]
By doing this step, you also enable other applications/programs disabled by this malware/grayware.

Step 4

Delete this registry key

[ 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\Policies
    • System
  • In HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Internet Explorer
    • Control Panel
  • In HKEY_CURRENT_USER\Software\Policies\Microsoft\Internet Explorer
    • Control Panel

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
    • Yahoo Messengger = "%System%\chrome.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Schedule
    • AtTaskMaxHours = "0"

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
    • From: Default_Page_URL = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"
      To: Default_Page_URL = ""http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
    • From: Default_Search_URL = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"
      To: Default_Search_URL = ""http://www.microsoft.com/isapi/redir.dll?prd=ie&ar=iesearch""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
    • From: Search Page = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"
      To: Search Page = ""http://www.microsoft.com/isapi/redir.dll?prd=ie&ar=iesearch""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
    • From: Start Page = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"
      To: Start Page = ""http://www.microsoft.com/isapi/redir.dll?prd={SUB_PRD}&clcid={SUB_CLSID}&pver={SUB_PVER}&ar=home""
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • From: Start Page = "http://h1.{BLOCKED}y.com/mygoogle0/index.html"
      To: Start Page = ""http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Shell = "Explorer.exe chrome.exe"
      To: Shell = ""Explorer.exe""

Step 7

Scan your computer with your Trend Micro product to delete files detected as WORM_YAHLOVER.RW. 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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