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Backdoor.Win32.PLUGX.DYSGUO

June 11, 2020
 Analysis by: Mc Justine De Guzman
 PLATFORM:

Windows

 OVERALL RISK RATING:
 REPORTED INFECTION:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

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

  TECHNICAL DETAILS

File Size:

25,600 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

02 Jun 2020

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:

  • %ProgramData%\AAM UpdatesrTw\AAM Updates.exe
  • %ProgramData%\AAM UpdatesrTw\hex.dll
  • %ProgramData%\AAM UpdatesrTw\adobeupdate.dat

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It adds the following processes:

  • %ProgramData%\AAM UpdatesrTw\AAM Updates.exe {random numbers}

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It creates the following folders:

  • %ProgramData%\AAM UpdatesrTw

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This contains application data for all users. This is usually C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit), or C:\Documents and Settings\All Users on Windows Server 2003(32-bit), 2000(32-bit) and XP.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • cTwEwEovsVjgufdrqqDS

Autostart Technique

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

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
AAM UpdatesrTw = %ProgramData%\AAM UpdatesrTw\AAM Updates.exe {random numbers}

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
AAM UpdatesrTw = %ProgramData%\AAM UpdatesrTw\AAM Updates.exe {random numbers}

Backdoor Routine

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

  • Create pipe name
  • Launch cmd.exe
  • Execute remote shell
  • Get drive information
  • Search for a certain file
  • Get the details of a file
    • Date
    • Size
    • Contents
  • Write a file
  • Create a folder
  • Check for the existence of a file
  • Launch new processes under a hidden Desktop
  • Copy file
  • Move file
  • Delete file
  • Rename file
  • Expand environment variables and replace with the values that the attacker desired
  • Get the directory containing malicious code
  • Get victim's information
    • System information
    • Memory usage status information
    • Operating System version information
    • Hostname and Username information
    • Screen resolution information
  • Create thread related to pipe communication
  • Exit process

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

  • {BLOCKED}.{BLOCKED}.104.38

Other Details

This Backdoor adds the following registry keys:

HKEY_LOCAL_MACHINE\Software\CLASSES\
ms-pu

HKEY_LOCAL_MACHINE\Software\CLASSES\
ms-pu\PROXY

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

15.906.08

FIRST VSAPI PATTERN DATE:

02 Jun 2020

VSAPI OPR PATTERN File:

15.907.00

VSAPI OPR PATTERN Date:

03 Jun 2020

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 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
    • AAM UpdatesrTw = "%ProgramData%\AAM UpdatesrTw\AAM Updates.exe" {random numbers}"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • AAM UpdatesrTw = "%ProgramData%\AAM UpdatesrTw\AAM Updates.exe" {random numbers}"

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.

  • In HKEY_LOCAL_MACHINE\Software\CLASSES\ms-pu
    • Default = ""
  • In HKEY_LOCAL_MACHINE\Software\CLASSES\ms-pu\PROXY
    • Default = ""

Step 6

Search and delete this file

[ 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.
  • %ProgramData%\AAM UpdatesrTw\AAM Updates.exe
  • %ProgramData%\AAM UpdatesrTw\hex.dll
  • %ProgramData%\AAM UpdatesrTw\adobeupdate.dat

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.
  • %ProgramData%\AAM UpdatesrTw

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.Win32.PLUGX.DYSGUO. 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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