PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • 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.

  TECHNICAL DETAILS

File Size: 494,080 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 05 Mar 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 adds the following processes:

  • "powershell" Get-MpPreference -verbose
  • {malware file path and name} "{path}"
  • "schtasks.exe" /create /f /tn "DSL Subsystem" /xml "%User Temp%\tmp6BCC.tmp"
  • "schtasks.exe" /create /f /tn "DSL Subsystem Task" /xml "%User Temp%\tmp9904.tmp"
  • "%System Root%\Program Files\Windows Media Player\wmpnetwk.exe"
  • %System%\svchost.exe -k LocalServiceAndNoImpersonation
  • %System%\svchost.exe -k WerSvcGroup

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local\Temp on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It creates the following folders:

  • %Program Files%\DSL Subsystem
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\Logs\{username}
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\Logs
  • %Windows%\ServiceProfiles\NetworkService\AppData\Local\Microsoft

(Note: %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000(32-bit), Server 2003(32-bit), XP, Vista(64-bit), 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit) , or C:\Program Files (x86) in Windows XP(64-bit), Vista(64-bit), 7(64-bit), 8(64-bit), 8.1(64-bit), 2008(64-bit), 2012(64-bit) and 10(64-bit).. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)

Other System Modifications

This Backdoor deletes the following files:

  • %Windows%\Tasks\DSL Subsystem Task.job
  • {malware file path and name}:Zone.Identifier
  • %Program Files%\DSL Subsystem\dslss.exe
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\DSL Subsystem\dslss.exe
  • %Windows%\Tasks\DSL Subsystem.job

(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000(32-bit), Server 2003(32-bit), XP, Vista(64-bit), 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit) , or C:\Program Files (x86) in Windows XP(64-bit), Vista(64-bit), 7(64-bit), 8(64-bit), 8.1(64-bit), 2008(64-bit), 2012(64-bit) and 10(64-bit).. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\
Microsoft\Windows Defender\Features
TamperProtection = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows Defender
DisableAntiSpyware = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows Defender\Real-Time Protection
DisableBehaviorMonitoring = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows Defender\Real-Time Protection
DisableOnAccessProtection = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows Defender\Real-Time Protection
DisableScanOnRealtimeEnable = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\
Microsoft\Windows\CurrentVersion\
Run
DSL Subsystem = "%Program Files%\DSL Subsystem\dslss.exe"

Dropping Routine

This Backdoor drops the following files:

  • %All Users Profile%\Microsoft\Network\Downloader\qmgr1.dat
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\run.dat
  • %All Users Profile%\Microsoft\Windows\DRM\drmstore.hds
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\task.dat
  • %AppDataLocal%\Microsoft\Media Player\CurrentDatabase_372.wmdb
  • %All Users Profile%\Microsoft\Network\Downloader\qmgr0.dat
  • %All Users Profile%\Microsoft\Windows\DRM\v3ks.sec
  • %AppDataLocal%\GDIPFONTCACHEV1.DAT
  • %Program Files%\DSL Subsystem\dslss.exe

(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). . %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Roaming on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name}\AppData\Local on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000(32-bit), Server 2003(32-bit), XP, Vista(64-bit), 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit) , or C:\Program Files (x86) in Windows XP(64-bit), Vista(64-bit), 7(64-bit), 8(64-bit), 8.1(64-bit), 2008(64-bit), 2012(64-bit) and 10(64-bit).)

Other Details

This Backdoor connects to the following possibly malicious URL:

  • http://iconboss26.{BLOCKED}s.net

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine: 9.850

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

Identify and terminate files detected as Backdoor.Win32.NANOCORE.THCOEBO

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 3

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\Wow6432Node\Microsoft\Windows Defender\Features
    • TamperProtection = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
    • DisableAntiSpyware = "1"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection
    • DisableBehaviorMonitoring = "1"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection
    • DisableOnAccessProtection = "1"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection
    • DisableScanOnRealtimeEnable = "1"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Run
    • DSL Subsystem = "%Program Files%\DSL Subsystem\dslss.exe"

Step 4

Search and delete these components

[ Learn More ]
There may be some components 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%\Microsoft\Network\Downloader\qmgr1.dat
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\run.dat
  • %All Users Profile%\Microsoft\Windows\DRM\drmstore.hds
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\task.dat
  • %AppDataLocal%\Microsoft\Media Player\CurrentDatabase_372.wmdb
  • %All Users Profile%\Microsoft\Network\Downloader\qmgr0.dat
  • %All Users Profile%\Microsoft\Windows\DRM\v3ks.sec
  • %AppDataLocal%\GDIPFONTCACHEV1.DAT
  • %Program Files%\DSL Subsystem\dslss.exe

Step 5

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.
  • %Program Files%\DSL Subsystem
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\Logs\{username}
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\Logs
  • %Windows%\ServiceProfiles\NetworkService\AppData\Local\Microsoft

Step 6

Scan your computer with your Trend Micro product to delete files detected as Backdoor.Win32.NANOCORE.THCOEBO. 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 the following Trend Micro Support pages for more information:

Step 7

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %Windows%\Tasks\DSL Subsystem Task.job
  • {malware file path and name}:Zone.Identifier
  • %Program Files%\DSL Subsystem\dslss.exe
  • %Application Data%\0EFADD19-2A94-41FB-8931-F2BBC5D61333\DSL Subsystem\dslss.exe
  • %Windows%\Tasks\DSL Subsystem.job


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