Analysis by: Christopher Daniel So
ALIASES:

Backdoor:Win32/Plugx (Microsoft), Backdoor.Korplug (Symantec), Backdoor.Win32.Gulpix.vir (Kaspersky), Win32/Korplug.GZ (ESET), W32/Gulpix.VIR!tr.bdr (Fortinet), Backdoor.Win32.Gulpix (Ikarus)

 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 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: Varies
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 19 Aug 2015
Payload: Compromises system security, 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%\nvdisps.dll
  • %User Temp%\nvdisps_user.dat

(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.)

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

  • Fast

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CLASSES_ROOT\FAST

It adds the following registry entries:

HKEY_CLASSES_ROOT\FAST
CLSID = "{random hex values}"

Backdoor Routine

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

  • Get drive information
  • Enumerate files
  • Create directories
  • Get file information
  • Read from a file
  • Write to a file
  • Copy, move, rename, delete files
  • Execute files
  • Lock workstation
  • Log off user
  • Restart/Shutdown system
  • Display a message box
  • Perfrom port mapping
  • Enumerate processes
  • Enumerate process modules
  • Terminate processes
  • Enumerate services
  • Get service information
  • Modify services
  • Start services
  • Delete services
  • Perform remote shell

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

  • http://{BLOCKED}.{BLOCKED}.81.131:443/update?id={id}
  • http://{BLOCKED}.{BLOCKED}.28.6:443/update?id={id}
  • http://app.{BLOCKED}ldfun.com:443/update?id={id}

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.864.07
FIRST VSAPI PATTERN DATE: 20 Aug 2015
VSAPI OPR PATTERN File: 11.865.00
VSAPI OPR PATTERN Date: 20 Aug 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

Restart in Safe Mode

[ Learn More ]

Step 3

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_CLASSES_ROOT
    • FAST

Step 4

Search and delete these files

[ Learn More ]
There may be some component 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.
  • %User Temp%\nvdisps.dll
  • %User Temp%\nvdisps_user.dat

Step 5

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