BKDR_PLUGX.ZTBF-A

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.

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.