Analysis by: Rhena Inocencio
 Modified by: Jed Valderama
ALIASES:

Backdoor:Win32/Plugx.A (Microsoft), Trojan.Win32.Generic.pak!cobra (Sunbelt), Backdoor.Win32.Plugx, Backdoor.Win32.Plugx (Ikarus)

 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 backdoor may be dropped by other malware.

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

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 284,436 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 20 Jul 2012
Payload: Connects to URLs/IPs

Arrival Details

This backdoor may be dropped by the following malware:

  • TROJ_PIDIEF.AMF

Installation

This backdoor drops the following files:

  • %System Root%\Documents and Settings\All Users\SxS\bug.log
  • %System Root%\Documents and Settings\All Users\SxSv\rc.exe - normal file (Microsoft Resource Compiler)
  • %System Root%\Documents and Settings\All Users\SxSv\rc.hlp - detected as TROJ_PLUGX.SME
  • %System Root%\Documents and Settings\All Users\SxSv\rcdll.dll - detected as TROJ_PLUGX.AF

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It creates the following folders:

  • %System Root%\Documents and Settings\All Users\SxS
  • %System Root%\Documents and Settings\All Users\SxSv

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

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\SxSv
Description = "SxSv"

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

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SxSv
ImagePath = ""%System Root%\Documents and Settings\All Users\SxSv\rc.exe" 200 0"

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

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

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

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CLASSES_ROOT\FAST

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SxSv

Backdoor Routine

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

  • Collect network information
  • Execute remote commands through Telnet
  • Impersonate user privileges
  • Log keystrokes

Dropping Routine

This backdoor drops the following file(s), which it uses for its keylogging routine:

  • %System Root%\Documents and Settings\All Users\SxSv\kl.log

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Other Details

This backdoor connects to the following possibly malicious URL:

  • bangzi.{BLOCKED}00dy.net
  • 111092231008.{BLOCKED}com.ixlink.netc

It deletes itself after execution.

NOTES:

This backdoor uses the normal file RC.EXE as a component to reconstruct itself after installation using its component files TROJ_PLUGX.SME and TROJ_PLUGX.AF.

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 9.274.03
FIRST VSAPI PATTERN DATE: 20 Jul 2012
VSAPI OPR PATTERN File: 9.275.00
VSAPI OPR PATTERN Date: 21 Jul 2012

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

Scan your computer with your Trend Micro product and note files detected as BKDR_PLUGX.AF

Step 3

Remove malware/grayware files that dropped/downloaded BKDR_PLUGX.AF

Step 4

Remove malware/grayware files dropped/downloaded by BKDR_PLUGX.AF

Step 5

Restart in Safe Mode

[ Learn More ]

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.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • SxSv
  • In HKEY_CLASSES_ROOT
    • FAST

Step 7

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.
  • %System Root%\Documents and Settings\All Users\SxS
  • %System Root%\Documents and Settings\All Users\SxSv

Step 8

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 Root%\Documents and Settings\All Users\SxSv\kl.log

Step 9

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