Modified by: Adrian Cofreros
ALIASES:

Trojan:Win32/Lethic.B(Microsoft),Win32/Lethic.AA trojan(NOD32),Backdoor.Win32.Azbreg.ydp(Kaspersky)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • 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: 79,360 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 30 Jan 2014
Payload: Drops files, Connects to URLs/IPs

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\swcode.exe
  • %System Root%\RECYCLER\proedit.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\swcode.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Windows Services Management = "%System Root%\RECYCLER\swcode.exe"

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

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Windows Remote Management = "%System Root%\RECYCLER\proedit.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "explorer.exe,%System Root%\RECYCLER\proedit.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 in the folder %System Root%\RECYCLER to Read only, Hidden, and System.

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

  • {BLOCKED}3.{BLOCKED}e.ru
  • {BLOCKED}4.{BLOCKED}e.ru

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

  SOLUTION

Minimum Scan Engine: 9.300
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.EN 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\swcode.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Windows Services Management = "%System Root%\RECYCLER\swcode.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Shell = "explorer.exe,%System Root%\RECYCLER\swcode.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Taskman = "%System Root%\RECYCLER\proedit.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Windows Remote Management = "%System Root%\RECYCLER\proedit.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Shell = "explorer.exe,%System Root%\RECYCLER\proedit.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

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