Threat Encyclopedia

BKDR_PLUGX.ZTBF-A

Publish date: June 25, 2014

ANALYSIS BY

Rhena Inocencio


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:

Dropped by other malware


This malware is part of a targeted attack against certain entities in Taiwan on June 2014, utilizing not only PlugX RAT malware but also the use of Dropbox. It uses Dropbox to update its C&C settings in order to listen and perform commands from a remote malicious user. Users affected by this malware may find the security of their systems compromised.

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

This backdoor may arrive bundled with malware packages as a malware component.

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

TECHNICAL DETAILS

File Size:

117,428 bytes

File Type:

Other

Memory Resident:

Yes

Initial Samples Received Date:

12 Jun 2014

Payload:

Connects to URLs/IPs

Arrival Details

This backdoor may arrive bundled with malware packages as a malware component.

Installation

This backdoor drops the following copies of itself into the affected system:

  • %All Users Profile%\DRM\RasTls\RasTls.DLL.msc

(Note: %All Users Profile% is the All Users or Common profile folder, which is C:\Documents and Settings\All Users in Windows 2000, XP, and Server 2003, and C:\ProgramData in Windows Vista and 7.)

It drops the following component file(s):

  • %All Users Profile%\DRM\RasTls.exe - non-malicious file used to load TROJ_PLUGX.ZTBF-A
  • %All Users Profile%\DRM\RasTls.DLL - detected as TROJ_PLUGX.ZTBF-A
  • %All Users Profile%\DRM\RasTls\{random file name}

(Note: %All Users Profile% is the All Users or Common profile folder, which is C:\Documents and Settings\All Users in Windows 2000, XP, and Server 2003, and C:\ProgramData in Windows Vista and 7.)

It creates the following folders:

  • %All Users Profile%\DRM

(Note: %All Users Profile% is the All Users or Common profile folder, which is C:\Documents and Settings\All Users in Windows 2000, XP, and Server 2003, and C:\ProgramData in Windows Vista and 7.)

It is injected into the following processes running in memory:

  • svchost.exe
  • msiexec.exe

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasT1s
ImagePath = "%All Users Profile%\DRM\RasTls.exe"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasT1s
DisplayName = "RasTls"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasT1s
Description = "RasTls"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasT1s
ObjectName = "LocalSystem'

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_RAST1S\
0000
Service = "RasT1s"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_RAST1S\
0000
DeviceDesc = "RasTls"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_RAST1S

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasT1s

Backdoor Routine

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

  • Manage files, registries, services and directories
  • Log keystrokes and active window
  • Restart/Reboot/Shutdown system
  • Enumerate processes
  • Terminate processes
  • Get drive information
  • Enumerate network resources
  • Set TCP connection state
  • Lock workstation
  • Display a message box
  • Perfrom port mapping
  • Capture screen
  • Perform remote shell

NOTES:

It connects to the following URL to acquire its C&C setting:

  • http://{BLOCKED}.{BLOCKED}xusercontent.com/s/0lkgew1wqqw6h13/20140512.txt

However, as of this writing, the server does not contain the expected file.

This backdoor will only perform its intended routine if the current date is March 5, 2014 or onwards.

SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

10.856.08

FIRST VSAPI PATTERN DATE:

12 Jun 2014

VSAPI OPR PATTERN File:

10.857.00

VSAPI OPR PATTERN Date:

12 Jun 2014

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

Remove the malware/grayware file dropped/downloaded by BKDR_PLUGX.ZTBF-A. (Note: Please skip this step if the threat(s) listed below have already been removed.)

Step 3

Restart in Safe Mode

[ Learn More ]

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.


  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root
    • LEGACY_RAST1S
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • RasT1s

Step 5

Search and delete this folder

[ 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.
 
  • %All Users Profile%\DRM

Step 6

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