Backdoor.Win32.ZEGOST.AB

April 15, 2019
 Analysis by: Carl Maverick Pascual
 ALIASES:

HEUR:Trojan.Win32.Generic (Kaspersky) ; a variant of Win32/Packed.NoobyProtect.O suspicious application (ESET-Nod32)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Downloaded from the Internet

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 steals certain information from the system and/or the user.

  TECHNICAL DETAILS

File Size:

1,389,568 bytes

File Type:

EXE, DLL

Memory Resident:

No

Initial Samples Received Date:

02 Apr 2019

Payload:

Connects to URLs/IPs, Steals information

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 copies of itself into the affected system:

  • %System%\AppleOSSMgr.exe

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

It drops the following files:

  • {Malware Directory}\$$a39494$$.bat -> deletes the original copies of itself
  • %System%\AppleOSSMgr.dll -> Detected also as Backdoor.Win32.ZEGOST.AB
  • %System%\AppleOSSMgr.dat -> Component file

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

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\ControlSet001\services\
AppleOSSMgr
Description = Provides support for switching between OS X and Windows

HKEY_LOCAL_MACHINE\ControlSet001\services\
AppleOSSMgr\Parameters
ServiceDll = %System%\AppleOSSMgr.dll

HKEY_LOCAL_MACHINE\ControlSet001\services\
AppleOSSMgr
ImagePath = %System%\svchost.exe -k netsvcs

HKEY_LOCAL_MACHINE\Microsoft\Windows NT\
CurrentVersion\Svchost
netsvcs = {Original Value}, AppleOSSMgr

Other System Modifications

This Backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
WinOldApp

Backdoor Routine

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

  • {BLOCKED}.{BLOCKED}.242.151:2014

Information Theft

This Backdoor steals the following information:

  • OS Information
  • Workstation Type

Other Details

This Backdoor does the following:

  • This backdoor has the following capabilities:
    • Modify Registry Entries
    • Enumerate Drives
    • Get Clipboard Contents
    • Remote Desktop
    • Screen Capture
    • Download Files
    • Upload Files
    • Video Capture
    • Remote command execution
    • Send and Receive Audio
    • Send and Receive Text via Chatbox

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.939.00

FIRST VSAPI PATTERN DATE:

14 Apr 2019

VSAPI OPR PATTERN File:

14.939.00

VSAPI OPR PATTERN Date:

14 Apr 2019

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
    • AppleOSSMgr

Step 4

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies
    • WinOldApp

Step 5

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