Analysis by: Rhena Inocencio
 Modified by: Abraham Latimer Camba

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

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

  TECHNICAL DETAILS

File Size: 295,736 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 20 Jul 2012

Arrival Details

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

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%\1.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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

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.)

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}.{BLOCKED}.231.6:443

  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

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
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • SxSq

Step 4

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\SxSq

Step 5

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.
  • %User Temp%\1.exe
  • %User Temp%\2.doc

Step 6

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