ALIASES:

ERROR (Microsoft); Trojan Horse (Symantec); Trojan.Win32.Scar.dkaj (Kaspersky); Trojan.Win32.Generic!BT (Sunbelt); Trojan horse Downloader.VB.BVM (AVG)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size: 77,824 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 24 Jul 2013

Arrival Details

This Trojan 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 Trojan creates the following folders:

  • %Windows%\Crystal

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

Autostart Technique

This Trojan registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\stuad

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\htuad

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\htoad

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\VB and VBA Program Settings\
RTR\TR

It adds the following registry entries:

HKEY_CURRENT_USER\Software\VB and VBA Program Settings\
RTR\TR
RT = ",,,,"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%System Root%\\{malware file name}.exe = "{random characters}"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\stuad
Description = "{random characters}"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\stuad
Description = "Transaction Coordinator"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\stuad
ErrorControl = "1"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\stuad
ImagePath = "%Windows%\Crystal\smss.exe /service"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\stuad
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\stuad
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\stuad
Type = "11"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htuad
Description = "{random characters}"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htuad
Description = "Transaction Coordinator"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htuad
ErrorControl = "1"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htuad
ImagePath = "%Windows%\msapps\csrss.exe /service"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htuad
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htuad
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htuad
Type = "11"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htoad
Description = "{random characters}"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htoad
Description = "Transaction Coordinator"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htoad
ErrorControl = "1"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htoad
ImagePath = "svshost.exe /service"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htoad
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htoad
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\htoad
Type = "11"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control
ServicesPipeTimeout = "271"

Dropping Routine

This Trojan drops the following files:

  • %System%\svshost

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

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine: 9.300

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

Restart in Safe Mode

[ Learn More ]

Step 3

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • stuad
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • htuad
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • htoad
  • In HKEY_CURRENT_USER\Software\VB and VBA Program Settings\RTR
    • TR

Step 4

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\VB and VBA Program Settings\RTR\TR
    • RT = ",,,,"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %System Root%\{malware file name}.exe = "{random characters}"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\stuad
    • Description = "{random characters}"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\stuad
    • Description = "Transaction Coordinator"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\stuad
    • ErrorControl = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\stuad
    • ImagePath = "%Windows%\Crystal\smss.exe /service"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\stuad
    • ObjectName = "LocalSystem"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\stuad
    • Start = "2"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\stuad
    • Type = "11"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htuad
    • Description = "{random characters}"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htuad
    • Description = "Transaction Coordinator"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htuad
    • ErrorControl = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htuad
    • ImagePath = "%Windows%\msapps\csrss.exe /service"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htuad
    • ObjectName = "LocalSystem"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htuad
    • Start = "2"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htuad
    • Type = "11"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htoad
    • Description = "{random characters}"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htoad
    • Description = "Transaction Coordinator"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htoad
    • ErrorControl = "1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htoad
    • ImagePath = "svshost.exe /service"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htoad
    • ObjectName = "LocalSystem"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htoad
    • Start = "2"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\htoad
    • Type = "11"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control
    • ServicesPipeTimeout = "271"

Step 5

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.
  • %System%\svshost

Step 6

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Windows%\Crystal

Step 7

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