BKDR_PLUGX.AG

October 09, 2012
 Analysis by: Rhena Inocencio
 ALIASES:

Backdoor:Win32/Plugx.A (Microsoft)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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 uses the default Windows folder icon to trick users into opening the file. Double-clicking the file executes this malware.

  TECHNICAL DETAILS

File Size:

302,627 bytes

File Type:

EXE

Initial Samples Received Date:

01 Aug 2012

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:

  • %System Root%\Documents and Settings\All Users\SxS\bug.log
  • %System Root%\Documents and Settings\All Users\SxSq\rc.exe
  • %System Root%\Documents and Settings\All Users\SxSq\rc.hlp
  • %System Root%\Documents and Settings\All Users\SxSq\rcdll.dll
  • %User Temp%\{random number}.exe
  • %User Temp%\2.doc

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.)

It creates the following folders:

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

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

It uses the default Windows folder icon to trick users into opening the file. Double-clicking the file executes this malware.

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\SxSq
Description = "SxSq"

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

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

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

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

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

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

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CLASSES_ROOT\FAST

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SxSq

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}ee.{BLOCKED}-show.org