Modified by: RonJay Kristoffer Caragay
ALIASES:

Trojan:Win32/Lethic.B (Microsoft); W32/Azbreg.AAHB!tr.bdr (Fortinet); TR/Crypt.Xpack.84287 (Antivir), Backdoor.Win32.Azbreg.aahb (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: 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.

  TECHNICAL DETAILS

File Size: 141,824 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 16 Jul 2014
Payload: Connects to URLs/IPs, Drops files, Modifies 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\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.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\S-1-5-21-0243556031-888888379-781863308-615643

(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:

  • a3631f1

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\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
6z4666 = "%System Root%\RECYCLER\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "explorer.exe,%System Root%\RECYCLER\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.exe"

Dropping Routine

This Trojan drops the following files:

  • %System Root%\RECYCLER\S-1-5-21-0243556031-888888379-781863308-615643\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.

This Trojan attempts to establish a connection to the following remote servers through TCP port 8800:

  • {BLOCKED}.{BLOCKED}sprox333.com:8800

The remote server may send data containing IP addresses to TROJ_LETHIC.AZB. Then, TROJ_LETHIC.AZB may send traffic to these IP addresses.

It does not listen for incoming connections.

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 10.936.04
FIRST VSAPI PATTERN DATE: 21 Jul 2014
VSAPI OPR PATTERN File: 10.937.00
VSAPI OPR PATTERN Date: 22 Jul 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

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 = "%System Root%\RECYCLER\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • 6z4666 = "%System Root%\RECYCLER\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Shell = "explorer.exe,%System Root%\RECYCLER\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.exe"

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\S-1-5-21-0243556031-888888379-781863308-615643\61bf266.exe
  • %System Root%\RECYCLER\S-1-5-21-0243556031-888888379-781863308-615643\Desktop.ini

Step 6

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\S-1-5-21-0243556031-888888379-781863308-615643

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_LETHIC.AZB. 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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