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WORM_DORKBOT.KZ

April 13, 2013
 ALIASES:

Worm:Win32/Dorkbot.AR (Microsoft), Trojan.Win32.Jorik.IRCbot.xkt (Kaspersky)

 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:

  • 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 executes then deletes itself afterward.

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:

257,024 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

13 Apr 2013

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 files:

  • {removable drive letter}:\snkb0ptz\Desktop.ini

It drops the following copies of itself into the affected system:

  • %Application Data%\{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 executes then deletes itself afterward.

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
{random letters}.exe = "%Application Data%\{random letters}.exe"

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

Propagation

This worm creates the following folders in all removable drives:

  • {removable drive letter}:\snkb0ptz

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

  • {removable drive letter}:\snkb0ptz\snkb0ptz.exe

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:

;{garbage characters}
{removable drive letter}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}
{removable drive letter}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}
{removable drive letter}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}

Download Routine

This worm connects to the following URL(s) to download its component file(s):

  • http://{BLOCKED}e.com/dl/202145748/705bd55/haha.html

It saves the files it downloads using the following names:

  • %User Temp%\{random letters}.exe

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

Other Details

This worm connects to the following possibly malicious URL:

  • {BLOCKED}4.{BLOCKED}ost.com
  • {BLOCKED}n.de
  • {BLOCKED}les.org
  • {BLOCKED}4.{BLOCKED}ost.com
  • {BLOCKED}sion-media.de

NOTES:

It drops shortcut files pointing to the copy of itself in removable drives. These dropped .LNK files use the names of the folders located on the said drives for their file names. It then sets the attributes of the original folders to Hidden to trick the user into clicking the .LNK files.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.838.07

FIRST VSAPI PATTERN DATE:

06 Apr 2013

VSAPI OPR PATTERN File:

9.839.00

VSAPI OPR PATTERN Date:

06 Apr 2013

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 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
    • {random letters}.exe = "%Application Data%\{random letters}.exe"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • {random letters}.exe = "%Application Data%\{random letters}.exe"

Step 4

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.
  • {removable drive letter}:\snkb0ptz

Step 5

Search and delete AUTORUN.INF files created by WORM_DORKBOT.KZ that contain these strings

[ Learn More ]
;{garbage characters}
{removable drive letter}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}
{removable drive letter}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}
{removable drive letter}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}

Step 6

Search and delete this file

[ Learn More ]

There may be some component 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.
  • %User Temp%\{random letters}.exe

Step 7

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