WORM_DORKBOT.SMM

 Analysis by: Abraham Latimer Camba

 ALIASES:

W32/Dorkbot.6D8E!tr (Fortinet), Trojan:Win32/Ircbrute (Microsoft), Trojan-Ransom.Win32.Blocker.azoo (Kaspersky), Trojan.Win32.Generic.pak!cobra (Sunbelt)

 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: Yes

  • In the wild: Yes

  OVERVIEW

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.

  TECHNICAL DETAILS

File Size:

207,360 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

30 Apr 2013

Payload:

Connects to URLs/IPs, Downloads files, Drops files, Compromises system security

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}:\snkb0ptz\Desktop.ini
  • {removable drive letter}:\{folder name}.lnk
  • {network drive letter}:\snkb0ptz\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}:\snkb0ptz
  • {network drive letter}:\snkb0ptz

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

  • snkb0ptz

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}:\snkb0ptz\snkb0ptz.exe

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

Backdoor Routine

This worm connects to any of the following IRC server(s):

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

It 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

Download Routine

This worm connects to the following website(s) to download and execute a malicious file:

  • http://{BLOCKED}e.com/dl/208146938/aab93b5/000660.html
  • http://{BLOCKED}e.com/dl/208146938/aab93b5/000660.html
  • http://{BLOCKED}e.com/dl/208146938/aab93b5/000660.html
  • http://{BLOCKED}e.com/dl/208146938/aab93b5/000660.html
  • http://{BLOCKED}3.{BLOCKED}e.com/get/2ad2d3a9d0b6f89fdf3a02cb988b7431e2e6a7dd/5180aa32/2/183ad0654f954a7a/c6811fa/000660
  • http://{BLOCKED}3.{BLOCKED}e.com/get/8ee83e2f2630eaf9a8ac9fd89d25367560101d66/5180a930/2/183ad0654f954a7a/c6811fa/000660
  • http://{BLOCKED}3.{BLOCKED}e.com/get/b7ccfa350b21feac3c194f7047a6e0de57a9cbe8/5180a9bd/2/183ad0654f954a7a/c6811fa/000660
  • http://{BLOCKED}3.{BLOCKED}e.com/get/f597281a91151992855fa801ab3e60c8875bb936/5180ab92/2/183ad0654f954a7a/c6811fa/000660
  • http://{BLOCKED}3.{BLOCKED}e.com/get/f597281a91151992855fa801ab3e60c8875bb936/5180ab92/2/183ad0654f954a7a/c6811fa/000660

It saves the files it downloads using the following names:

  • %User Temp%\{random}.exe - detected as WORM_DORKBOT.SME

(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 deletes the initially executed copy of itself

NOTES:
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.

  SOLUTION

Minimum Scan Engine:

9.300

VSAPI OPR PATTERN File:

9.889.00

VSAPI OPR PATTERN Date:

01 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

Remove malware/grayware files dropped/downloaded by WORM_DORKBOT.SMM

     
    • WORM_DORKBOT.SME

Step 3

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

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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

Step 6

Search and delete these folders

[ 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
  • {network drive letter}:\snkb0ptz

Step 7

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

Step 8

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

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

Step 9

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