Analysis by: Hazel Ann Poligratis

ALIASES:

PWS:Win32/Bzub (Microsoft), Mal/Buzb-A (SOPHOS_LITE)

 PLATFORM:

Windows

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

  • Threat Type: File infector

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 1,748,533 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 20 Jun 2018

Arrival Details

This File infector 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 File infector drops the following copies of itself into the affected system and executes them:

  • %Application Data%\Microsoft\Messenger\Extension\WdExt.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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 creates the following folders:

  • %Application Data%\Temp

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.)

Autostart Technique

This File infector adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Windows Defender Extension = "%Application Data%\Microsoft\Defender\launch.exe"

Other System Modifications

This File infector adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{GUID}

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{GUID}
StubPath = "%System%\mscaps.exe" /s /n /i:U shell32.dll

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{GUID}
ComponentID = DirectShow

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{GUID}
Version = 1,125,2406,1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{GUID}
Locale = *

File Infection

This File infector infects the following files:

  • .exe files in shared folders and removable drives

Dropping Routine

This File infector drops the following files:

  • %Application Data%\Temp\mydll.dll
  • %Application Data%\Temp\{Username}{number}.bat
  • %%Application Data%\Microsoft\Identities\{Username}\arc.dll
  • %Application Data%\Microsoft\Windows\Addins\att.dll
  • %Application Data%\Microsoft\Common\Shared\dis.dll
  • %Application Data%\Microsoft\Shared\Modules\fil.dll
  • %Application Data%\Microsoft\Repairs\sha.dll
  • %Application Data%\Microsoft\Caches\Files\usd.dll
  • %Application Data%\Microsoft\Defender\launch.exe
  • %System%\mscaps.exe
  • %System%\wtime32.dll

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

Other Details

This File infector connects to the following URL(s) to check for an Internet connection:

  • windowsupdate.microsoft.com
  • update.microsoft.com

It connects to the following possibly malicious URL:

  • a.gwas.{BLOCKED}l.sh
  • {BLOCKED}krCmkrZgqoLAYHBgbGJ6hHhsbmZw.g.s
  • a-gwas-01.{BLOCKED}p.net
  • a-gwas-01.{BLOCKED}s.org

It deletes itself after execution.

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 14.330.04
FIRST VSAPI PATTERN DATE: 21 Jun 2018
VSAPI OPR PATTERN File: 14.331.00
VSAPI OPR PATTERN Date: 22 Jun 2018

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ 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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Windows Defender Extension = "%Application Data%\Microsoft\Defender\launch.exe"

Step 5

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.

  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{GUID}

Step 6

Search and delete this folder

[ 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.
  • %Application Data%\Temp

Step 7

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.
  • %Application Data%\Microsoft\Messenger\Extension\WdExt.exe
  • %%Application Data%\Microsoft\Identities\{Username}\arc.dll
  • %Application Data%\Microsoft\Windows\Addins\att.dll
  • %Application Data%\Microsoft\Common\Shared\dis.dll
  • %Application Data%\Microsoft\Shared\Modules\fil.dll
  • %Application Data%\Microsoft\Repairs\sha.dll
  • %Application Data%\Microsoft\Caches\Files\usd.dll
  • %Application Data%\Microsoft\Defender\launch.exe
  • %System%\mscaps.exe
  • %System%\wtime32.dll

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as PE_WINDEX.C-O. 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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