WORM_YAHLOVER.XA

 Analysis by: Vincent Martin Hermosura

 ALIASES:

Mal/Sohana-A (Sophos_Lite), Trojan horse Downloader.Agent2.WQU (AVG), Worm.Win32.AutoIt.sp (Kaspersky), Worm:Win32/YahLover.C (Microsoft), Win32/AutoRun.Autoit.P worm (Nod32), W32.Svich (Norton)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


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 drives. These dropped copies use the names of the folders located on the said drives for their file names. 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:

771,838 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

21 Apr 2014

Arrival Details

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.

Installation

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

  • %Windows%\scvhost.exe
  • %System%\scvhost.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows.. %System% is the Windows system folder, which is usually C:\Windows\System32.)

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%\scvhost.exe"

Other System Modifications

This worm modifies the following registry keys:

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

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

Propagation

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

  • {removable drive letter}:\New Folder.exe
  • {removable drive letter}:\scvhost.exe

It drops copies of itself in all drives. These dropped copies use the names of the folders located on the said drives for their file names.

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]
Open=scvhost.exe
Shellexe cute=scvhost.exe
Shell\Open\command=scvhost.exe
Shell=Open

Other Details

This worm connects to the following possibly malicious URL:

  • {BLOCKED}gle.{BLOCKED}h.com
  • {BLOCKED}gle1.{BLOCKED}h.com

NOTES:
It drops copies of itself in all drives. These dropped copies use the names of the folders located on the said drives for their file names.

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

10.740.06

FIRST VSAPI PATTERN DATE:

21 Apr 2014

VSAPI OPR PATTERN File:

10.741.00

VSAPI OPR PATTERN Date:

21 Apr 2014

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 WORM_YAHLOVER.XA using the 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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Yahoo Messengger = "%System%\scvhost.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\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Shell = "Explorer.exe scvhost.exe"
      To: Shell = Explorer.exe

Step 5

Search and delete AUTORUN.INF files created by WORM_YAHLOVER.XA that contain these strings

[ Learn More ]


[Autorun]
Open=scvhost.exe
Shellexe cute=scvhost.exe
Shell\Open\command=scvhost.exe
Shell=Open

Step 6

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