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Worm.Win32.RIMECUD.I

June 23, 2023
 Analysis by: Francesca Villasanta
 ALIASES:

Trojan:Win32/Rimecud.A (MICROSOFT)

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware, Propagates via removable drives


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

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size:

130,889 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

15 Jun 2023

Payload:

Compromises system security, Steals information, Connects to URLs/IPs, Modifies system registry, Deletes files

Arrival Details

This Worm 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 Worm drops the following copies of itself into the affected system:

  • %User Profile%\kohwe.exe → attributes are set to READONLY, HIDDEN, and SYSTEM

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It adds the following processes:

  • %System%\svchost.exe

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

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • `=08+10

It injects itself into the following processes as part of its memory residency routine:

  • svchost.exe → executed by the malware

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Taskman = %User Profile%\kohwe.exe

Other System Modifications

This Worm deletes the following files:

  • %User Profile%\kohwe.exe → if the executed file path and name is not "%User Profile%\kohwe.exe"

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

Propagation

This Worm creates the following folders in all removable drives:

  • torpide

It drops the following copy(ies) of itself in all removable drives:

  • {Removable Drive}\torpide\gengems.exe

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[autorun]
;garbage characters
shell\open\command=torpide\gengems.exe
;garbage characters
action=Open folder to view files using Windows Explorer
;garbage characters
Shell\Open\Command=torpide\gengems.exe
;garbage characters
shellexecute=torpide\gengems.exe
;garbage characters
shell\explore\command=torpide\gengems.exe
;garbage characters
icon=SHELL32.dll,4
;garbage characters
open=torpide\gengems.exe
;garbage characters
USEAUTOPLAY=1
;garbage characters

Backdoor Routine

This Worm executes the following commands from a remote malicious user:

  • Update / Remove self
  • Download and execute arbitrary files
  • USB Spreader
  • Visit a URL / Display pop-up advertisements

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

  • udp://{BLOCKED}trule.com:11111
  • udp://{BLOCKED}esask.net:11111
  • udp://{BLOCKED}gesonest.com:11111
  • udp://{BLOCKED}ince.kz:11111
  • udp://{BLOCKED}lks.su:11111

Information Theft

This Worm gathers the following data:

  • IP Address
  • Network Setting
  • Operation System
  • Admin Rights
  • Country
  • Port Used
  • Username / Hostname

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

18.524.03

FIRST VSAPI PATTERN DATE:

22 Jun 2023

VSAPI OPR PATTERN File:

18.525.00

VSAPI OPR PATTERN Date:

23 Jun 2023

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 NT\CurrentVersion\Winlogon
    • Taskman = "%User Profile%\kohwe.exe"

Step 5

Search and delete AUTORUN.INF files created by Worm.Win32.RIMECUD.I that contain these strings

[ Learn More ]
  • [autorun]
  • ;garbage characters
  • shell\open\command=torpide\gengems.exe
  • ;garbage characters
  • action=Open folder to view files using Windows Explorer
  • ;garbage characters
  • Shell\Open\Command=torpide\gengems.exe
  • ;garbage characters
  • shellexecute=torpide\gengems.exe
  • ;garbage characters
  • shell\explore\command=torpide\gengems.exe
  • ;garbage characters
  • icon=SHELL32.dll,4
  • ;garbage characters
  • open=torpide\gengems.exe
  • ;garbage characters
  • USEAUTOPLAY=1
  • ;garbage characters

Step 6

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.  
  • %User Profile%\kohwe.exe
  • {Removable Drive}:\torpide\gengems.exe

Step 7

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.
  • {Removable Drive}:\torpide

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Worm.Win32.RIMECUD.I. 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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