WORM_DORKBOT.EMS

 Analysis by: Rika Joi Gregorio

 ALIASES:

Trojan.Win32.Jorik.IRCbot.xab(Kaspersky), Backdoor:Win32/IRCbot.FY(Microsoft), W32.SillyDC(Norton), a variant of Win32/Injector.WLI trojan(Eset)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Via physical/removable drives, Downloaded from the Internet, Dropped by other malware, Propagates via removable drives


This worm arrives via removable drives. 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 connects to Internet Relay Chat (IRC) servers. It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size:

569,344 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

13 Nov 2014

Payload:

Connects to URLs/IPs

Arrival Details

This worm arrives via removable drives.

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 Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops the following files:

  • {drive}:\Desktop.ini
  • {drive}:\{folder name}.lnk

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

  • byYStt

It stays memory-resident by creating remote threads:

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

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

Propagation

This worm creates the following folders in all removable drives:

  • {drive}:\byYstt

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

  • {drive}:\byYstt\byYStt.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 codes}
[autorun]
{garbage codes}
open={drive}:\byYstt\byYStt.exe
{garbage codes}
icon=%SystemRoot%\system32\SHELL32.dll,7
{garbage codes}
UseAutoPlay=1
{garbage codes}
shell\Explore\Command={drive}:\byYstt\byYStt.exe
{garbage codes}
shell\open\Command={drive}:\byYstt\byYStt.exe
{garbage codes}

Backdoor Routine

This worm connects to any of the following Internet Relay Chat (IRC) servers:

  • sp.{BLOCKED}p.kz

It joins any of the following IRC channel(s):

  • #id

It executes the following commands from a remote malicious user:

  • Block DNS
  • Create processes
  • Download other files
  • Insert iFrame tags into HTML files
  • Join an IRC channel
  • Log in to FTP sites
  • Perform Slowloris, UDP, and SYN flooding
  • Run Reverse Socks4 proxy server
  • Send MSN Messenger messages
  • Steal login credentials
  • Update itself
  • Visit a web site

NOTES:

This worm creates .LNK (shortcut) files using folder names found in removable drives. It then hides the original folder tricking users to click .LNK files. This .LNK files point out to a dropped copy of itself in the removable drive.

It terminates itself in the following conditions:

  • When executed in the following Virtual Environments:
    • QEMU
    • Virtual
    • VMWare
    • VBox
    • Anubis Sandox
    • CWSandbox
    • JoeBox
  • When the following module is loaded:
    • dbghelp.dll (ThreatExpert)
    • sbiedll.dll (SandBox)

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

11.274.03

FIRST VSAPI PATTERN DATE:

13 Nov 2014

VSAPI OPR PATTERN File:

11.275.00

VSAPI OPR PATTERN Date:

14 Nov 2014

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

Step 5

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.
  • {drive}:\byYstt

Step 6

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.
  • {drive}:\Desktop.ini
  • {drive}:\{folder name}.lnk

Step 7

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

[ Learn More ]

{garbage codes}
[autorun]
{garbage codes}
open={drive}:\byYstt\byYStt.exe
{garbage codes}
icon=%SystemRoot%\system32\SHELL32.dll,7
{garbage codes}
UseAutoPlay=1
{garbage codes}
shell\Explore\Command={drive}:\byYstt\byYStt.exe
{garbage codes}
shell\open\Command={drive}:\byYstt\byYStt.exe
{garbage codes}

Step 8

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