Analysis by: Michael John Marcos
ALIASES:

Backdoor: Win32/Layrui.A (Microsoft), Win32/Autoit.NFV trojan (ESET)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This backdoor deletes autostart registry entries associated with the processes it terminates to completely disable applications.

It deletes the file(s) associated with the process(es) it terminates. It does the said routine to completely disable programs and applications.

  TECHNICAL DETAILS

File Size: 442927 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 03 Apr 2013
Payload: Compromises system security, Connects to URLs/IPs, Downloads files

Installation

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

  • %Windows%\system32\svihost.exe

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

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Updates = "%Windows%\system32\svihost.exe"

Other System Modifications

This backdoor deletes the following files:

  • %Windows%\system32\update.exe
  • %Windows%\system32\server.txt
  • %Windows%\server.txt
  • %Windows%\system32\check.txt

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

It adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Policies\
Microsoft\Internet Explorer\Control Panel
Homepage = 0

HKEY_LOCAL_MACHINE\Software\Policies\
Microsoft\Internet Explorer\Control Panel
Homepage = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 0

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 0

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableTaskMgr = 0

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = 0

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Internet Explorer\Main
Start Page = "http://autokiemthe.com"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Start Page = "http://autokiemthe.com"

It deletes autostart registry entries associated with the processes it terminates to completely disable applications.

It deletes the following registry keys:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Updates =

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Update =

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Update =

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Updates =

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Internet Explorer\Main
Window Title =

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Window Title =

Process Termination

This backdoor deletes the file(s) associated with the process(es) it terminates. It does the said routine to completely disable programs and applications.

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://{BLOCKED}viet.com/bot/dunghoitaisao.php
  • http://{BLOCKED}viet.com/bot/update.exe
  • http://{BLOCKED}uyen.info/bot/dunghoitaisao.php
  • http://{BLOCKED}uyen.info/bot/update.exe

  SOLUTION

Minimum Scan Engine: 9.700

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

Restart in Safe Mode

[ Learn More ]

Step 3

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 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\CurrentVersion\Run
    • Windows Updates = "%Windows%\system32\svihost.exe"
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main
    • Start Page = "http://autokiemthe.com"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
    • Start Page = "http://autokiemthe.com"

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.
  • %Windows%\system32\svihost.exe

Step 6

Scan your computer with your Trend Micro product to delete files detected as BKDR_LAYRUI.B. 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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