BKDR_FYNLOS.S

 Analysis by: Sabrina Lei Sioting

 ALIASES:

Backdoor:Win32/Fynloski.A (Microsoft), Backdoor.Graybird (Symantec), Backdoor.Win32.Fynloski.A (Sunbelt), W32/Fynloski.XA!tr (Fortinet), Trojan.Win32.CDur (Ikarus), Win32/Fynloski.AA (Eset), 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:

  • 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 modifies certain registry entries to disable Security Center functions. Doing this allows this malware to execute its routines without being detected. It disables Task Manager, Registry Editor, and Folder Options. It bypasses the Windows firewall. This allows the malware to perform its intended routine without being detected by an installed firewall.

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

It logs a user's keystrokes to steal information.

  TECHNICAL DETAILS

File Size:

258,048 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

20 Jun 2011

Payload:

Steals information

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:

  • %Application Data%\VIA\vc.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:

  • %Application Data%\dclogs
  • %Application Data%\VIA

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

  • DC_MUTEX-3W64SLL

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
VIAChipset = "%Application Data%\VIA\vc.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe,%Application Data%\VIA\vc.exe"

(Note: The default value data of the said registry entry is %System%\userinit.exe,.)

Other System Modifications

This backdoor adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableLUA = "0"

It adds the following registry keys as part of its installation routine:

HKEY_CURRENT_USER\Software\DC3_FEXEC

It modifies the following registry entries to disable Security Center functions:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Security Center
AntiVirusDisableNotify = "1"

(Note: The default value data of the said registry entry is 0.)

It creates the following registry entry(ies) to disable Task Manager, Registry Tools and Folder Options:

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

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

It modifies the following registry entries to disable the Windows Firewall settings:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile
EnableFirewall = "0"

(Note: The default value data of the said registry entry is 1.)

Backdoor Routine

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

  • Capture video from webcam
  • Change MSN messenger status
  • Download and execute files
  • Download updated copy of itself
  • Upload files
  • Display message box
  • Empty Recycle Bin
  • List active windows
  • Log keystrokes
  • Manipulate the following:
  • -Clipboard
  • -Desktop
  • -Files
  • -Mouse clicks
  • -Processes
  • -Regitries
  • -Start button
  • -System clock
  • -System tray
  • -Taskbar
  • Modify system's host file
  • Open and close CD-ROM drive door
  • Record sounds
  • Remote shell command
  • Steal passwords
  • Uninstall programs

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

  • {BLOCKED}604.no-ip.org
  • {BLOCKED}x-update.zapto.org

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.

Stolen Information

The stolen information is saved in the following file:

  • %Application Data%\dclogs\{date executed}-{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

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

Identify and delete files detected as BKDR_FYNLOS.S using either the Startup Disk or Recovery Console

[ Learn More ]

Step 3

To enable Registry Editor, Task Manager, and Folder options:

  1. Open Notepad. To do this:
    • For Windows 2000, XP, and Server 2003 users:
      Click Start > Run, type Notepad in the text box provided, then press Enter.
    • For Windows Vista and 7 users:
      Click Start > type Notepad On Error Resume Next Set shl = WScript.CreateObject("WScript.Shell") shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableTaskMgr" shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableRegistryTools" , then press Enter.
  2. Copy and paste the following script:
  3. Save this file as On Error Resume Next Set shl = WScript.CreateObject("WScript.Shell") shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableTaskMgr" shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableRegistryTools"  On Error Resume Next Set shl = WScript.CreateObject("WScript.Shell") shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableTaskMgr" shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableRegistryTools" C:RESTORE.VBS.
  4. Click Start>Run again, type C:RESTORE.VBS in the text box provided, then press Enter.
  5. Click Yes at the On Error Resume Next Set shl = WScript.CreateObject("WScript.Shell") shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableTaskMgr" shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableRegistryTools"  On Error Resume Next Set shl = WScript.CreateObject("WScript.Shell") shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableTaskMgr" shl.RegDelete "HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\\DisableRegistryTools" prompt of the message box to execute the .VBS file.

Step 4

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_CURRENT_USER\Software
    • DC3_FEXEC

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
    • VIAChipset = "%Application Data%\VIA\vc.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
    • EnableLUA = "0"

Step 6

Restore this modified 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Userinit = "%System%\userinit.exe,%Application Data%\VIA\vc.exe"
      To: Userinit = %System%\userinit.exe,
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center
    • From: AntiVirusDisableNotify = "1"
      To: AntiVirusDisableNotify = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile
    • From: EnableFirewall = "0"
      To: EnableFirewall = 1

Step 7

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
%Application Data%\VIA

Step 8

Scan your computer with your Trend Micro product to delete files detected as BKDR_FYNLOS.S. 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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