Analysis by: Sammy Chua

ALIASES:

Backdoor:Win32/Kriskynote.A (Microsoft), Backdoor:Win32/Kriskynote.B (Microsoft), Backdoor.Korplug.B (Symantec)

 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: Dropped by other malware, Downloaded from the Internet

This PlugX variant is found in compromised releases of some legitimate online games.

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

  TECHNICAL DETAILS

File Size: 442,892 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 31 Dec 2014
Payload: Drops files, Terminates processes

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:

  • %User Temp%\tmp2B.tmp - detected as BKDR_PLUGX.ZTBL-EC, executable image, will be deleted
  • %User Temp%\tmp2C.tmp - will be used to replace the loader and deleted
  • %User Temp%\tmp2D.tmp - detected as BKDR_PLUGX.ZTBL-EC, dll image, will be deleted
  • %Application Data%\dat2E.tmp - will be deleted
  • %Application Data%\dat2F.tmp - will be deleted
  • %Application Data%\dat30.tmp - will be deleted
  • %System%\NtUserEx.dat
  • %System%\NtUserEx.dll

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp 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.. %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.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It adds the following processes:

  • rundll32.exe
  • svchost.exe

It injects codes into the following process(es):

  • created rundll32.exe
  • created svchost.exe

Autostart Technique

This backdoor registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}
ImagePath = "%SystemRoot%\System32\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}
DisplayName = "automaticallydevice"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}
Description = "Monitoring of hardwares and automatically updates the device drivers"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}
Type = "32"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}\Parameters
ServiceDll = "%System%\NtUserEx.dll"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}\Parameters
ServiceMain = sqlite3_aggregate_num

It registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}\Parameters

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{service name}

Backdoor Routine

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

  • Copy, move, rename, delete files
  • Create directories
  • Create files
  • Enumerate files
  • Execute files
  • Get drive information
  • Get file information
  • Open and modify files
  • Enumerate TCP and UDP connections
  • Enumerate network resources
  • Set TCP connection state
  • Lock workstation
  • Log off user
  • Restart/Reboot/Shutdown system
  • Display a message box
  • Perfrom port mapping
  • Enumerate processes
  • Get process information
  • Terminate processes
  • Enumerate registry keys
  • Create registry keys
  • Delete registry keys
  • Copy registry keys
  • Enumerate registry entries
  • Modify registry entries
  • Delete registry values
  • Screen capture
  • Delete services
  • Enumerate services
  • Get service information
  • Modify services
  • Start services
  • Perform remote shell
  • Host Telnet server
  • Connect to a database server and execute SQL statement
  • Log keystrokes and active window

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

  • {BLOCKED}4.playdr2.tw/update?id={random} - {inaccessible}
  • {BLOCKED}2.playdr2.tw:443/update?id={random}
  • {BLOCKED}3.playdr2.tw:53/update?id={random} - {inaccessible}
  • {BLOCKED}4.playdr2.tw:1080/update?id={random} - {inaccessible}

NOTES:

The {service name} is obtained by reading the "netsvcs" value of the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Svchost.

The loader file is replaced by a modified "cleaned" copy which the malware executes after dropping the other files.

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 11.406.04
FIRST VSAPI PATTERN DATE: 12 Jan 2015
VSAPI OPR PATTERN File: 11.407.00
VSAPI OPR PATTERN Date: 13 Jan 2015

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

Scan your computer with your Trend Micro product and note files detected as BKDR_PLUGX.ZTBL-EC

Step 4

Restart in Safe Mode

[ Learn More ]

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}
    • ImagePath = "%SystemRoot%\System32\svchost.exe -k netsvcs"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}
    • DisplayName = "automaticallydevice"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}
    • Description = "Monitoring of hardwares and automatically updates the device drivers"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}
    • Start = "2"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}
    • Type = "32"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}
    • ObjectName = "LocalSystem"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}\Parameters
    • ServiceDll = "%System%\NtUserEx.dll"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}\Parameters
    • ServiceMain = sqlite3_aggregate_num

Step 6

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}\Parameters
    • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\{service name}

Step 7

Search and delete these files

[ 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.
  • %System%\NtUserEx.dll
  • %System%\NtUserEx.dat

Step 8

Search and delete the files detected as BKDR_PLUGX.ZTBL-EC

*Note: Some component files may be 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.

To stop the malware/grayware from running when certain files are opened:

For Windows 2000, Windows XP, and Windows Server 2003:

  1. Right-click Start then click Search....
  2. In the File name* input box, type the name of the file that was detected earlier.
  3. In the Look In drop-down list, select My Computer then press Enter.
  4. Once located, select the file then press SHIFT+DELETE to delete it.
    *Note: The file name input box title varies depending on the Windows version (e.g. Search for files or folders named or All or part of the file name.).

For Windows Vista, Windows 7, Windows Server 2008, Windows 8, Windows 8.1, and Windows Server 2012 (R2):

  1. Open a Windows Explorer window.
    • For Windows Vista, 7, and Server 2008 users, click Start>Computer.
    • For Windows 8, 8.1, and Server 2012 users, right-click on the lower left corner of the screen,then click File Explorer.
  2. In the Search Computer/This PC input box, type the name of the file that was detected earlier.
  3. Once located, select the file then press SHIFT+DELETE to delete it.
    *Note: Read the following Microsoft page if these steps do not work on Windows 7.

Step 9

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_PLUGX.ZTBL-EC. 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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