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BKDR_FYNLOSKI.YYSWT

October 24, 2016
 Analysis by: John Kevin Sanchez
 ALIASES:

Backdoor:Win32/Fynloski.M (Microsoft), Backdoor.DarkKomet.r4 (CAT-QuickHeal), MSIL/Injector.GGF!tr (Fortinet)

 PLATFORM:

Windows

 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 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 executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

It logs a user's keystrokes to steal information.

  TECHNICAL DETAILS

File Size:

563,712 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

19 Oct 2016

Payload:

Steals information, Compromises system security, Drops files

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 files:

  • %Application Data%\DcjeswNd\PJGzURi.exe.lnk
  • %Application Data%\dclogs\{YYYY-MM-DD-S}.dc - log file where keystrokes and other information are written

(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 copies of itself into the affected system:

  • %Application Data%\DcjeswNd\PJGzURi.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 creates the following folders:

  • %Application Data%\DcjeswNd
  • %Application Data%\dclogs

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

  • DC_MUTEX-{random 7 alphanumeric characters}

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
shell = %Application Data%\DcjeswNd\PJGzURi.exe,explorer.exe

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\DC3_FEXEC

Backdoor Routine

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

  • Disable RegistryTools
  • Disable TaskMgr
  • Disable Control Panel
  • List disk drives
  • List webcams and monitor/capture video
  • Change MSN Messenger status & modify contact list
  • Shutdown, Restart, Log off or Lock computer
  • Empty Recycle Bin
  • Visit arbitrary C&C servers
  • List active windows
  • Remote shell command
  • Download and execute files
  • Download updated copy of itself
  • Upload files
  • Log keystrokes
  • Refresh or delete logs
  • Modify system's host file
  • Record and play sounds
  • Open and close CD-ROM drive door
  • Steal passwords
  • Get torrent files
  • Refresh Wifi
  • Uninstall programs
  • Start and control chat sessions
  • Monitor activity by Remote Desktop Protocol
  • DDOS Flooding
  • 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
  • Lessen system security level by:
    • Disabling update notification
    • Disabling AV notification
    • Disabling firewall
    • Disabling services
    • Disabling LUA notification

It connects to the following websites to send and receive information:

  • {BLOCKED}igboy101.no-ip.biz:1604

Information Theft

This backdoor gathers the following data:

  • Admin rights
  • Computer/User name
  • Language/Country
  • Operating System information
  • RAM used
  • Web Cam information

It logs a user's keystrokes to steal information.

Other Details

This backdoor does the following:

  • The malware logs the following information:
    • Program
    • Time
    • Keystrokes

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.846.04

FIRST VSAPI PATTERN DATE:

19 Oct 2016

VSAPI OPR PATTERN File:

12.847.00

VSAPI OPR PATTERN Date:

20 Oct 2016

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 NT\CurrentVersion\Winlogon
    • shell = %Application Data%\DcjeswNd\PJGzURi.exe,explorer.exe

Step 5

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 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.
  • %Application Data%\DcjeswNd
  • %Application Data%\dclogs

Step 7

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