Analysis by: Vincent Martin Hermosura
ALIASES:

Backdoor.Win32.DarkKomet.xyk (Kaspersky), Backdoor:Win32/Fynloski.A (Microsoft), Backdoor.Graybird (Symmantec), Generic BackDoor.xa (Mcafee), Backdoor.Win32.Fynloski.A (v) (Sunbelt), BDS/DarkKomet.GR (Antivir), W32/Downloader.C.gen!Eldorado (Authentium), Backdoor.Fynloski.C (Bitdefender), W32/DarkKomet.ID!tr.bdr (Fortinet), W32/Downloader.C.gen!Eldorado (generic, not disinfectable) (Fprot), Backdoor.Win32.Zegost (Ikarus), Win32/Fynloski.AA trojan (Esset), Trj/Packed.B (Panda), Backdoor.DarkKomet (Vba32)

 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: No

  • 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 deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 774,656 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 02 Sep 2014
Payload: Compromises system security, Steals information, Drops files, Displays message/message boxes

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 copies of itself into the affected system and executes them:

  • %User Profile%\My Documents\MSDCSC\msdcsc.exe

(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 adds the following processes:

  • notepad.exe

It creates the following folders:

  • %Application Data%\dclogs
  • %User Profile%\My Documents\MSDCSC

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

  • DC_MUTEX-3QJJWRG

It injects codes into the following process(es):

  • notepad.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\Run
MicroUpdate = "%User Profile%\My Documents\MSDCSC\msdcsc.exe"

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\DC3_FEXEC

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = "dword:00000001"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = "dword:00000001"

Backdoor Routine

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

  • Lessen system security level
  • 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

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

  • {BLOCKED}k123.ddns.net

Dropping Routine

This backdoor drops the following file(s), which it uses for its keylogging routine:

  • %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.)

Information Theft

This backdoor gathers the following data:

  • Admin rights
  • Computer/User name
  • Language/Country
  • Operating System information
  • Network configuration
  • Screen Resolution

Other Details

This backdoor deletes the initially executed copy of itself

NOTES:

It sets the attribute of the following files to System and Hidden:

  • {malware path and filename}
  • {malware path}
  • %User Profile%\My Documents\MSDCSC
  • %User Profile%\My Documents\MSDCSC\msdcsc.exe

It displays a message box below as a payload.

  SOLUTION

Minimum Scan Engine: 9.700

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
    • MicroUpdate = "%User Profile%\My Documents\MSDCSC\msdcsc.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • DisableRegistryTools = "dword:00000001"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • DisableTaskMgr = "dword:00000001"

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%\dclogs
  • %User Profile%\My Documents\MSDCSC

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

Step 8

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