Analysis by: Mohammed Malubay
ALIASES:

Trojan.Dllhijacker(QUICKHEAL); Trojan.Win32.ZAccess.bg(SUNBELT);

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

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: 1,668,608 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 14 Jun 2021
Payload: Modifies system registry, Drops files, Executes files, Others

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:

  • %All Users Profile%\Temp\svchost.exe → loads mscoree.dll
  • %All Users Profile%\Temp\mscoree.dll → detected as Backdoor.Win32.SHADOWPAD.ZAIF-B (loads mscoree.dll.mui)
  • %All Users Profile%\Temp\mscoree.dll.mui → detected as Backdoor.Win32.SHADOWPAD.ZBIF-B (main routine)

(Note: %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit). )

It adds the following processes:

  • If its execution path is %All User Profile%\Temp:
    • %All Users Profile%\Temp\svchost.exe
    • %System%\winlogon.exe

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It creates the following folders:

  • %All Users Profile%\Temp

(Note: %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit). )

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

  • Global\nflvjnpfbblrtvbndlnrnttdx

It injects codes into the following process(es):

  • %System%\winlogon.exe

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

Other System Modifications

This Backdoor adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\ipn
ipn = {Hex Values}

Backdoor Routine

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

  • Download and execute arbitrary codes

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

  • http://davires.pu{BLOCKED}.com:8080

As of this writing, the said servers are currently inaccessible.

Other Details

This Backdoor adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\ipn

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
NzThbz

It requires the following additional components to properly run:

  • %All Users Profile%\Temp\mscoree.dll.mui → detected as Backdoor.Win32.SHADOWPAD.ZBIF-B

(Note: %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit). )

It adds and runs the following services:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
services\svchost
ImagePath = %All Users Profile%\Temp\svchost.exe

It does the following:

  • Its execution path needs to be in %All Users Profile%\Temp to perform its malicious routine
  • Checks for the existence of:
    • %All Users Profile%\ptdpbdpp\ttxtnz\bbfltjvd\dxrpltfb

(Note: %All Users Profile% is the common user's profile folder, which is usually C:\Documents and Settings\All Users on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\ProgramData on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit). )

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 16.804.04
FIRST VSAPI PATTERN DATE: 26 Jun 2021
VSAPI OPR PATTERN File: 16.805.00
VSAPI OPR PATTERN Date: 27 Jun 2021

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, and then 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\SYSTEM\ControlSet001\services
    • svchost

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_LOCAL_MACHINE\SOFTWARE\ipn
    • ipn = {Hex Values}

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
    • ipn
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft
    • NzThbz

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.
  • %All Users Profile%\Temp\svchost.exe
  • %All Users Profile%\Temp\mscoree.dll
  • %All Users Profile%\Temp\mscoree.dll.mui

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.
  • %All Users Profile%\Temp

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.Win32.SHADOWPAD.ZAIF-B. 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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