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WORM_DORKBOT.ABM
Aliases: Worm:Win32/Dorkbot.AM (Microsoft), PWS-Zbot.gen.ary (McAfee), Worm.Win32.Dorkbot (Sunbelt)
Malware type: Worm
Destructive: No
Platform: Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)
Encrypted: Yes
In the wild: Yes

Infection Channel: Propagates via flashdrives, Propagates via network shares, Downloaded from the Internet, Dropped by other malware

This worm arrives by connecting affected removable drives to a system. It arrives by accessing affected shared networks. 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 an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

It executes commands from a remote malicious user, effectively compromising the affected system.

It deletes the initially executed copy of itself.


File size: varies
File type: EXE
Memory resident: Yes
Initial samples received date: 02 May 2013
Payload: Downloads files, Drops files, Compromises system security, Connects to URLs/IPs

Arrival Details

This worm arrives by connecting affected removable drives to a system.

It arrives by accessing affected shared networks.

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 component file(s):

  • {removable drive letter}:\snkb0pt\Desktop.ini
  • {removable drive letter}:\{folder name}.lnk
  • {network drive letter}:\snkb0pt\Desktop.ini
  • {network drive letter}:\{folder name}.lnk

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

  • %Application Data%\{random}.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 creates the following folders:

  • {removable drive letter}:\snkb0pt
  • {network drive letter}:\snkb0pt

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • snkb0pt

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

Propagation

This worm drops copies of itself in network drives such as the following:

  • {network drive letter}:\snkb0pt\snkb0pt.exe

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

  • {removable drive letter}:\snkb0pt\snkb0pt.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 or network drive letter}:\snkb0pt\snkb0pt.exe
;{garbage characters}
{removable or network drive letter}:\snkb0pt\snkb0pt.exe
;{garbage characters}
{removable or network drive letter}:\snkb0pt\snkb0pt.exe
;{garbage characters}

Backdoor Routine

This worm executes the following commands from a remote malicious user:

  • Update itself
  • Join/Leave an IRC channel
  • Download other files
  • Perform Slowloris, UDP, and SYN flooding
  • Create processes

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • f.{BLOCKED}on.pl
  • s.{BLOCKED}b.pl
  • {BLOCKED}sbh.org
  • {BLOCKED}h.com
  • h.{BLOCKED}ws.su
  • o.{BLOCKED}adio.su
  • {BLOCKED}h.net
  • {BLOCKED}sphere.su
  • {BLOCKED}obeat.su
  • {BLOCKED}us.kei.su

Other Details

This worm deletes the initially executed copy of itself

NOTES:

It downloads files from its C&C servers and saves it as %User Temp%\{random}.exe.

As of this writing, there are no files downloaded upon connecting to the server.

It drops shortcut files pointing to its copy in removable and network 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.

It connects to any of the following IRC servers:

  • {BLOCKED}.{BLOCKED}.71.238:9000
  • {BLOCKED}.{BLOCKED}.173.154:9000
  • {BLOCKED}.{BLOCKED}.86.198:9000

Minimum scan engine: 9.300
First VSAPI Pattern File: 9.894.03
First VSAPI Pattern Release Date: 03 May 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

Scan your computer with your Trend Micro product and note files detected as WORM_DORKBOT.ABM

Step 3

Restart in Safe Mode

Step 4

Delete this registry value

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

Step 5

Search and delete these folders

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}:\snkb0pt
  • {network drive letter}:\snkb0pt

Step 6

Search and delete this file

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}:\{folder name}.lnk
  • {network drive letter}:\{folder name}.lnk

Step 7

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

  • ;{garbage characters}
  • {removable or network drive letter}:\snkb0pt\snkb0pt.exe
  • ;{garbage characters}
  • {removable or network drive letter}:\snkb0pt\snkb0pt.exe
  • ;{garbage characters}
  • {removable or network drive letter}:\snkb0pt\snkb0pt.exe
  • ;{garbage characters}

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_DORKBOT.ABM. 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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Analysis By: Rhena Inocencio