Analysis by: Ricardo III Valdez
ALIASES:

Trojan:Win32/Hider.gen (MICROSOFT)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • 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.

  TECHNICAL DETAILS

File Size: 235,008 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 12 Dec 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:

  • %System%\exe{Current System Time}.tmp → Deleted afterwards
  • %System%\isass.exe → If not found on the system

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

It adds the following processes:

  • %System%\isass.exe {Malware File Path}\{Malware Filename}.exe

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

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
isass = %System%\isass.exe → If the service CSNetManagerXp is not created

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
isass = %System%\isass.exe → If the service CSNetManagerXp is not created

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\HideFileExt
UncheckedValue = 1

(Note: The default value data of the said registry entry is 0.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\SuperHidden
UncheckedValue = 0

(Note: The default value data of the said registry entry is 1.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = 1

(Note: The default value data of the said registry entry is 0.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = 0

(Note: The default value data of the said registry entry is 1.)

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
exefile
(Default) = File Folder

(Note: The default value data of the said registry entry is Application.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer
GlobalAssocChangedCounter = 36

(Note: The default value data of the said registry entry is 35.)

Other Details

This Trojan adds and runs the following services:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\CSNetManagerXp
Image Path = "%System%\isass.exe"

It does the following:

  • It closes a window named CeylonSpyNextXp.
  • It checks if username is SYSTEM
    • if no, starts the created service.
    • if yes, terminates the running service (CSNetManagerXp) and then starts it again using the current process.
  • It checks if username is LocalSystem
    • If yes, it creates a window named CeylonSpyNextXp

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 18.128.04
FIRST VSAPI PATTERN DATE: 12 Dec 2022
VSAPI OPR PATTERN File: 18.129.00
VSAPI OPR PATTERN Date: 13 Dec 2022

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • isass = %System%\isass.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • isass = %System%\isass.exe

Step 5

Restore this modified 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\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\HideFileExt
    • UncheckedValue = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\SuperHidden
    • UncheckedValue = 0
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • HideFileExt = 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • ShowSuperHidden = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\exefile
    • (default) = File Folder
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer
    • GlobalAssocChangedCounter = 36

Step 6

Disable this malware service

[ Learn More ]
  • CSNetManagerXp

Step 7

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.
  • %System%\exe{Current System Time}.tmp
  • %System%\isass.exe

Step 8

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