Analysis by: Nikko Tamana
ALIASES:

Trojan:Win32/Lethic.B (Microsoft), Trojan-Proxy.Win32.Lethic.bko (Kaspersky), Win32/Lethic.AA trojan (NOD32),

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • 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. It may be downloaded by other malware/grayware from remote sites.

  TECHNICAL DETAILS

File Size: 125,952 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 01 Nov 2013
Payload: 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.

It may be downloaded by the following malware/grayware from remote sites:

  • WORM_DORKBOT.WRF

Installation

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

  • %System Root%\RECYCLER\{Random SID}\xyzpro00.exe

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

It drops the following non-malicious file:

  • %System Root%\RECYCLER\{Random SID}\Desktop.ini

(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\{Random SID}

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

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

  • xyzpro00

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_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
xyzpro00.exe = "%System Root%\RECYCLER\{Random SID}\xyzpro00.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "explorer.exe,%System Root%\RECYCLER\{Random SID}\xyzpro00.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Taskman = "%System Root%\RECYCLER\{Random SID}\xyzpro00.exe"

NOTES:

This Trojan attempts to establish a connection to the following remote servers through TCP port 3300:

  • dq.{BLOCKED}xies1123.ru:3300
  • a119-12-209-91.{BLOCKED}m.com:3300

The remote host responds with the IP address it will contact and the traffic to TROJ_LETHIC.WRF. TROJ_LETHIC.WRF will then send the traffic to the IP address sent by the remote host. It does not listen for incoming connections. It may also request the malware to delete itself from the system.

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 10.380.03
FIRST VSAPI PATTERN DATE: 01 Nov 2013
VSAPI OPR PATTERN File: 10.381.00
VSAPI OPR PATTERN Date: 02 Nov 2013

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

Remove the malware/grayware file that dropped/downloaded TROJ_LETHIC.WRF

    • WORM_DORKBOT.WRF

Step 3

Identify and delete files detected as TROJ_LETHIC.WRF using the Recovery Console

[ 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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • xyzpro00.exe = "%System Root%\RECYCLER\{Random SID}\xyzpro00.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Shell = "explorer.exe,%System Root%\RECYCLER\{Random SID}\xyzpro00.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Taskman = "%System Root%\RECYCLER\{Random SID}\xyzpro00.exe"

Step 5

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. %System Root%\RECYCLER\{Random SID}

Step 6

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