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Threat Encyclopedia

BKDR_SHOTODOR.A

ANALYSIS BY

Alvin Bacani


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:
INFORMATION EXPOSURE:

  • Threat Type:Backdoor

  • Destructiveness:No

  • Encrypted: Yes

  • In the wild: Yes

OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


This malware makes use of “garbage” strings, which in actual hides the malicious code. The said malicious code is an obfuscated AutoIt script.

To get a one-glance comprehensive view of the behavior of this Backdoor, refer to the Threat Diagram shown below.

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It adds certain registry entries to disable the Task Manager. This action prevents users from terminating the malware process, which can usually be done via the Task Manager.

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

It modifies the Internet Explorer Zone Settings.

It logs a user's keystrokes to steal information.

TECHNICAL DETAILS

File Size:

1,235,361 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

08 Oct 2013

Payload:

Connects to URLs/IPs, Steals information, Compromises system security

Arrival Details

This backdoor 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 backdoor drops the following file(s)/component(s):

  • %User Profile%\WXVIL\RXBWDEDJ.dat - deleted after execution; contains obfuscated AutoScript
  • %User Profile%\WXVIL\762677.JUB - detected as BKDR_SHOTODOR.A
  • %User Profile%\WXVIL\settings.ini - config file
  • %User Profile%\WXVIL\481456.dat - encrypted file
  • %User Profile%\WXVIL\328774.dat - encrypted file

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

It drops the following non-malicious file:

  • %User Profile%\WXVIL\GIPYL.exe - non malicious AutoIt file

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

It creates the following folders:

  • %User Profile%\WXVIL
  • %Application Data%\dclogs

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %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 adds the following mutexes to ensure that only one of its copies runs at any one time:

  • DC_MUTEX-B2FTUQZ

It stays memory-resident by injecting codes into the following processes:

  • RegSvcs.exe (v2.0.50727)
  • RegSvcs.exe (v4.0.30319)
  • Default Internet Browser (e.g. iexplore.exe, firefox.exe, chrome.exe)

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
WXVIL = "%User Profile%\WXVIL\start.vbs"

It drops the following files:

  • %User Profile%\WXVIL\3562.vbs
  • %User Profile%\WXVIL\start.cmd
  • %User Profile%\WXVIL\start.vbs - runs the file "start.cmd"

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

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\DC3_FEXEC

It adds the following registry entries to disable the Task Manager:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = "1"

Backdoor Routine

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

  • Capture video from webcam
  • Change MSN Messenger & MSN contact list status
  • Empty Recycle Bin
  • List active windows
  • Remote shell command
  • Download and execute files
  • Download updated copy of itself
  • Upload files
  • Log keystrokes
  • Modify system's host file
  • Record sounds
  • Open and close CD-ROM drive door
  • Steal passwords
  • Get torrent files
  • Refresh Wifi
  • Uninstall programs
  • Manipulate the following:
    • Browser
    • Clipboard
    • Desktop
    • Dialog Box
    • Files
    • Folders
    • Mouse clicks
    • Processes
    • Registries
    • Services
    • Shutdown button options
    • Start button
    • System clock
    • System tray
    • Taskbar

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

  • http://root.{BLOCKED}a.ru:3162

Web Browser Home Page and Search Page Modification

This backdoor modifies the Internet Explorer Zone Settings.

Information Theft

This backdoor gathers the following data:

  • Admin rights
  • Computer/User name
  • Language/Country
  • Operating System information

It logs a user's keystrokes to steal information.

Stolen Information

The stolen information is saved in the following file:

  • %Application Data%\dclogs\{Current Date}-{Number}.dc

(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.)

SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

10.328.01

FIRST VSAPI PATTERN DATE:

08 Oct 2013

VSAPI OPR PATTERN File:

10.329.00

VSAPI OPR PATTERN Date:

09 Oct 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 key

[ 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
    • DC3_FEXEC = ""

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\RunOnce
    • WXVIL = "%User Profile%\WXVIL\start.vbs"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • DisableTaskMgr = "1"

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.
  • %User Profile%\WXVIL
  • %Application Data%\dclogs

Step 6

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