Analysis by: Maria Emreen Viray

ALIASES:

Trojan-Downloader.Win64.Agent.yj (KASPERSKY);

 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

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

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 executes then deletes itself afterward.

It does not have any propagation routine.

It does not have any backdoor routine.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 132,096 bytes
File Type: DLL
Memory Resident: Yes
Initial Samples Received Date: 18 Aug 2021
Payload: Steals information, Connects to URLs/IPs, Downloads files

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 adds the following processes:

  • %Windows%\explorer.exe /root, %System%\cmd.exe → loads downloaded %User Temp%\uc.dll

(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).)

It executes then deletes itself afterward.

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Command Processor
AutoRun = rundll32.exe "%User Temp%\uc.dll", out & exit

Propagation

This Trojan does not have any propagation routine.

Backdoor Routine

This Trojan does not have any backdoor routine.

Rootkit Capabilities

This Trojan does not have rootkit capabilities.

Download Routine

This Trojan accesses the following websites to download files:

  • http://web.{BLOCKED}c.o-r.kr/wp-includes/css/dist/nux/home/?act=wbi&id={Computername}&ver={OS Architecture}
  • http://web.{BLOCKED}c.o-r.kr/wp-includes/css/dist/nux/home/?act=paydb&id={Computername}&ver={OS Architecture}
  • http://web.{BLOCKED}c.o-r.kr/wp-includes/css/dist/nux/home/?act=paydl&id={Computername}&ver={OS Architecture}
  • http://web.{BLOCKED}c.o-r.kr/wp-includes/css/dist/nux/home/?act=sets&id={Computername}&ver={OS Architecture}
  • http://web.{BLOCKED}c.o-r.kr/wp-includes/css/dist/nux/home/?act=ucd&id={Computername}&ver={OS Architecture}

It saves the files it downloads using the following names:

  • %User Temp%\m.dll
  • %User Temp%\ht.tr
  • %User Temp%\sp.dll
  • %User Temp%\s.dll
  • %User Temp%\uc.dll

(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).)

As of this writing, the said sites are inaccessible.

Information Theft

This Trojan gathers the following data:

  • Username
  • Computername
  • OS Architecture
  • Contents of the following file:
    • %User Temp%\w.x

(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).)

Stolen Information

This Trojan sends the gathered information via HTTP POST to the following URL:

  • http://web.{BLOCKED}c.o-r.kr/wp-includes/css/dist/nux/home/up.php?id={Computername}

    NOTES:

This Trojan does the following:

  • Continues with routine:
    • If it is loaded by splwow64.exe
    • If URLs are still accessible
  • Attempts to delete the following after execution:
    • files:
      • %User Temp%\m.dll
      • %User Temp%\ht.tr
      • %User Temp%\sp.dll
      • %User Temp%\s.dll
      • %User Temp%\uc.dll
      • %User Temp%\w.x
    • registry entry:
      • HKEY_CURRENT_USER\Software\Microsoft\Command Processor
        AutoRun = rundll32.exe "%User Temp%\uc.dll", out & exit

    This Trojan does not exploit any vulnerability.

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 16.970.06
FIRST VSAPI PATTERN DATE: 16 Sep 2021
VSAPI OPR PATTERN File: 16.971.00
VSAPI OPR PATTERN Date: 17 Sep 2021

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.XXPE50FFF047

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

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\Command Processor
    • AutoRun = rundll32.exe "%User Temp%\uc.dll", out & exit

Step 5

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.
  • %User Temp%\m.dll
  • %User Temp%\ht.tr
  • %User Temp%\sp.dll
  • %User Temp%\s.dll
  • %User Temp%\uc.dll
  • %User Temp%\w.x

Step 6

Scan your computer with your Trend Micro product to delete files detected as Trojan.Win64.KGHSPY.ZKIH. 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:


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