TROJ_LETHIC.EW

February 10, 2014
 Modified by: Jimelle Monteser
 ALIASES:

Trojan:Win32/Lethic.B (Microsoft), Win32/Lethic.AA trojan (NOD32)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Downloaded from the Internet

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:

96,768 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

30 Jan 2014

Payload:

Connects to URLs/IPs, Drops 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 drops the following copies of itself into the affected system:

  • %System Root%\RECYCLER\wpnedit.exe

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It creates the following folders:

  • %System Root%\RECYCLER

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It stays memory-resident by creating remote threads:

  • explorer.exe

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Taskman = "%System Root%\RECYCLER\wpnedit.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Window Remote Managements = "%System Root%\RECYCLER\wpnedit.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "explorer.exe, %System Root%\RECYCLER\wpnedit.exe"

Dropping Routine

This Trojan drops the following files:

  • %System Root%\RECYCLER\Desktop.ini

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

NOTES:

This Trojan sets the file attributes of the dropped copy %System Root%\RECYCLER\wpnedit.exe to Read only, Hidden, and System.

It attempts to establish a connection to the following remote server:

  • {BLOCKED}5.{BLOCKED}e.ru

The remote server may send data containing IP addresses to TROJ_LETHIC.EW. Then, TROJ_LETHIC.EW may send traffic to these IP addresses. However, as of this writing, the said site is inaccessible.

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

10.574.02

FIRST VSAPI PATTERN DATE:

30 Jan 2014

VSAPI OPR PATTERN File:

10.575.00

VSAPI OPR PATTERN Date:

31 Jan 2014

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Identify and delete files detected as TROJ_LETHIC.EW using either the Startup Disk or Recovery Console

[ Learn More ]

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\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Taskman = %System Root%\RECYCLER\wpnedit.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Window Remote Managements = %System Root%\RECYCLER\wpnedit.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Shell = explorer.exe,%System Root%\RECYCLER\wpnedit.exe

Step 4

Search and delete this folder

[ 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.  
  • %System Root%\RECYCLER

Step 5

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 Root%\RECYCLER\Desktop.ini

Step 6

Scan your computer with your Trend Micro product to delete files detected as TROJ_LETHIC.EW. 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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