Analysis by: Jaime Benigno Reyes
ALIASES:

Worm:Win32/Dorkbot.I (Microsoft); Win32/Dorkbot.B worm (Nod32)

 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 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 deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 421,888 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 31 Jul 2014

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 and executes them:

  • %Application Data%\ScreenSaverPro.scr
  • %Application Data%\temp.bin
  • %Application Data%\Microsoft\{6 random letters}.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

It drops the following files:

  • {removable drive letter}\ACCOUNT.XLS.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\ACCOUNT.XLSX.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\AGREEMENT.DOC.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\AGREEMENT.DOCX.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\CONTACT.OAB.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\CONTACT.OST.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\CONTACT.PAB.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\CONTACT.PST.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\PROJECT.PPT.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe
  • {removable drive letter}\PROJECT.PPTX.LNK - shortcut pointing to {removable drive letter}\{15 random letters}.exe

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
Screen Saver Pro 3.1 = "%Application Data%\ScreenSaverPro.scr"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{6 random letters} = "%Application Data%\Microsoft\{6 random letters}.exe"

Other System Modifications

This worm adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_STISVC\
0000\Control
ActiveService = "stisvc"

Propagation

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

  • {removable drive letter}\{15 random letters}.exe

Other Details

This worm connects to the following possibly malicious URL:

  • http://{BLOCKED}.{BLOCKED}v.com
  • http://{BLOCKED}.{BLOCKED}n.com
  • http://{BLOCKED}.{BLOCKED}ato.com

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine: 9.700

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

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\Microsoft\Windows\CurrentVersion\Run
    • Screen Saver Pro 3.1 = "%Application Data%\ScreenSaverPro.scr"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {6 random letters} = "%Application Data%\Microsoft\{6 random letters}.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_STISVC\0000\Control
    • ActiveService = "stisvc"

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.
  • {removable drive letter}\ACCOUNT.XLS.LNK
  • {removable drive letter}\ACCOUNT.XLSX.LNK
  • {removable drive letter}\AGREEMENT.DOC.LNK
  • {removable drive letter}\AGREEMENT.DOCX.LNK
  • {removable drive letter}\CONTACT.OAB.LNK
  • {removable drive letter}\CONTACT.OST.LNK
  • {removable drive letter}\CONTACT.PAB.LNK
  • {removable drive letter}\CONTACT.PST.LNK
  • {removable drive letter}\PROJECT.PPT.LNK
  • {removable drive letter}\PROJECT.PPTX.LNK

Step 6

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