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Threat Encyclopedia

BKDR_PLUGX.BUT

ANALYSIS BY

Abraham Latimer Camba


PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

OVERALL RISK RATING:
DAMAGE POTENTIAL:
DISTRIBUTION POTENTIAL:
REPORTED INFECTION:

  • Threat Type:Backdoor

  • Destructiveness:No

  • Encrypted: Yes

  • In the wild: Yes

OVERVIEW

Infection Channel:

Dropped by other malware


This malware is a remote access tool (RAT) known as PlugX. It is one of the most common malware used in carrying out targeted attacks. The targeted attacks it has been involved in are mostly directed towards government institutions in Japan.

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

This backdoor may be dropped by other malware.

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:

3,072 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

24 Aug 2012

Payload:

Drops files, Steals information, Connects to URLs/IPs

Arrival Details

This backdoor may be dropped by the following malware:

  • BKDR_PLUGX.SME

Installation

This backdoor drops the following files:

  • All Users' %User Profile%\Gf\boot.ldr - detected as TROJ_PLUGX.SME
  • All Users' %User Profile%\Gf\NvSmart.exe - a legitimate NVIDIA (NVIDIA Smart Maximise Helper Host)
  • All Users' %User Profile%\SxS\bug.log - malware's error logs

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It drops the following copies of itself into the affected system:

  • All Users' %User Profile%\Gf\NvSmartMax.dll

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It creates the following folders:

  • All Users' %User Profile%\Gf
  • All Users' %User Profile%\SxS

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It injects itself into the following processes as part of its memory residency routine:

  • 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\Gf
Description = "Gf"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf
DisplayName = "Gf"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf
ImagePath = ""All Users' %User Profile%\Gf\NvSmart.exe" 200 0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf
Type = "110"

Other System Modifications

This backdoor adds the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf\Enum

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Gf\Security

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
FAST

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
FAST
CLSID = "{random hex values}"

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
  • Log keystrokes and active window
  • Enumerate TCP and UDP connections
  • Enumerate network resources
  • Set TCP connection state
  • Lock workstation
  • Log off user
  • Restart/Reboot 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
  • Connect to a database server and execute SQL statement
  • Host Telnet server

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

  • http://{BLOCKED}-save.{BLOCKED}d.com
  • http://{BLOCKED}tdns.net

Information Theft

This backdoor logs a user's keystrokes to steal information.

Stolen Information

This backdoor saves the stolen information in the following file:

  • {All Users' Profile}\Gf\kl.log

NOTES:

This backdoor is loaded each time the legitimate file NVSMART.EXE is executed.

The backdoor routines and C&C server this backdoor connects to depends on the contents of the loaded TROJ_PLUGX.SME.

SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

9.346.04

FIRST VSAPI PATTERN DATE:

24 Aug 2012

VSAPI OPR PATTERN File:

9.347.00

VSAPI OPR PATTERN Date:

25 Aug 2012

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove the malware/grayware file that dropped/downloaded BKDR_PLUGX.BUT

Step 3

Remove malware files dropped/downloaded by BKDR_PLUGX.BUT

Step 4

Restart in Safe Mode

[ Learn More ]

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_LOCAL_MACHINE\SOFTWARE\Classes
    • FAST
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • Gf

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.
  • {All Users'  Profile}\Gf
  • {All Users' Profile}\SxS

Step 7

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