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WORM_DORKBOT.LS

September 06, 2013
 Modified by: Anthony Joe Melgarejo
 ALIASES:

Trojan:Win32/Ircbrute (Microsoft), Trojan.Win32.Ircbrute (Vipre), W32/Nomkesh.C (Fortinet), Trojan.Win32.Ircbrute (Ikarus), Win32/Nomkesh.C worm (ESET),

 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 via removable drives. 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 deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

204,288 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

01 May 2013

Arrival Details

This worm arrives via removable drives.

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 copies of itself into the affected system and executes them:

  • %Application Data%\{random file name}.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.)

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

Propagation

This worm creates the following folders in all removable drives:

  • {removable drive}:\snkb0ptz

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

  • {network drive}:\snkb0ptz\snkb0ptz.exe

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

  • {removable drive}:\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 or network drive}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}
{removable or network drive}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}
{removable or network drive}:\snkb0ptz\snkb0ptz.exe
;{garbage characters}

Other Details

This worm connects to the following possibly malicious URL:

  • {BLOCKED}.{BLOCKED}on.pl
  • {BLOCKED}.{BLOCKED}b.pl
  • {BLOCKED}h.org

It deletes the initially executed copy of itself

NOTES:

It drops shortcut files pointing to the copy of itself 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.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.890.03

FIRST VSAPI PATTERN DATE:

01 May 2013

VSAPI OPR PATTERN File:

9.891.00

VSAPI OPR PATTERN Date:

02 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.LS

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete the registry entry with an unknown data 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.

  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run

Step 5

Search and delete these files

[ 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 or network drive}:\snkb0ptz

Step 6

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

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

Step 7

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