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BKDR_PLUGX.AH

March 25, 2013
 Analysis by: Sabrina Lei Sioting
 ALIASES:

Backdoor:Win32/Plugx.A (Microsoft), Backdoor.Korplug (Symentec), Troj/Plugx-B (Sophos), Backdoor.Win32.Plugx (Ikarus), Win32/Korplug.W trojan (Eset),

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

 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. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size:

259,072 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

07 Jan 2013

Arrival Details

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

It 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:

  • %ProgramData%\SxS\bug.log
  • %ProgramData%\SxSi\kl.log
  • %System Root%\Users\All Users\SxS\bug.log
  • %System Root%\Users\All Users\SxSi\kl.log

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This is usually C:\ProgramData in Windows Vista and 7, or C:\Program Files on Windows 2000, XP (32-bit), and Server 2003, or C:\Program Files (x86) on Windows XP (64-bit).. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It drops the following non-malicious files:

  • %ProgramData%\SxSi\rc.exe
  • %System Root%\Users\All Users\SxSi\rc.exe

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This is usually C:\ProgramData in Windows Vista and 7, or C:\Program Files on Windows 2000, XP (32-bit), and Server 2003, or C:\Program Files (x86) on Windows XP (64-bit).. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It creates the following folders:

  • %ProgramData%\SxS
  • %ProgramData%\SxSi
  • %System Root%\Users\All Users\SxS
  • %System Root%\Users\All Users\SxSi

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This is usually C:\ProgramData in Windows Vista and 7, or C:\Program Files on Windows 2000, XP (32-bit), and Server 2003, or C:\Program Files (x86) on Windows XP (64-bit).. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi
Type = "110"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi
ImagePath = "%ProgramData%\SxSi\rc.exe" 200 0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi
DisplayName = "SxSi"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi
Description = "SxSi"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\SxSi

Other System Modifications

This backdoor adds the following registry entries as part of its installation routine:

HKEY_CLASSES_ROOT\FAST
CLSID = "{hex values}"

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

It adds the following registry keys as part of its installation routine:

HKEY_CLASSES_ROOT\FAST

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
FAST

Backdoor Routine

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

  • http://{BLOCKED}irectme.net/update?id=00107f08

Dropping Routine

This backdoor drops the following files:

  • %ProgramData%\SxSi\rc.hlp
  • %ProgramData%\SxSi\rcdll.dll
  • %System Root%\Users\All Users\SxSi\rc.hlp
  • %System Root%\Users\All Users\SxSi\rcdll.dll

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This is usually C:\ProgramData in Windows Vista and 7, or C:\Program Files on Windows 2000, XP (32-bit), and Server 2003, or C:\Program Files (x86) on Windows XP (64-bit).. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.642.04

FIRST VSAPI PATTERN DATE:

07 Jan 2013

VSAPI OPR PATTERN File:

9.643.00

VSAPI OPR PATTERN Date:

08 Jan 2013

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\SOFTWARE\Classes
    • FAST
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services
    • SxSi

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.
  • %ProgramData%\SxS
  • %ProgramData%\SxSi
  • %System Root%\Users\All Users\SxS
  • %System Root%\Users\All Users\SxSi

Step 5

Scan your computer with your Trend Micro product to delete files detected as BKDR_PLUGX.AH. 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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