Analysis by: Jimelle Monteser
ALIASES:

Backdoor:Win32/Kelihos.F (Microsoft), Backdoor.Win32.Hlux.bodz (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: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This worm 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: 835,088 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 18 Dec 2013

Arrival Details

This worm arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
{random parameter 1}{random parameter 2} = "{malware path and file name}"

Other System Modifications

This worm adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
DefaultCompressedRecord = "{random value}"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
RecordModifiedMax = "{random value}=="

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
FlagsModifiedValid = "0"

HKEY_CURRENT_USER\Software\TansuTCP
ActiveModifiedTheme = "{random value}"

HKEY_CURRENT_USER\Software\TansuTCP
SizeCompletedValid = "{random value}=="

HKEY_CURRENT_USER\Software\TansuTCP
InfoPlayedCurrent = "0"

Propagation

This worm drops the following copy(ies) of itself in all removable drives:

  • {Removable Drive Letter}:\{random file name}.exe

Dropping Routine

This worm drops the following files:

  • {Removable Drive Letter}:\{folder name}.lnk - if folder exists in removable drive
  • {Removable Drive Letter}:\Shortcut to {random file name}.lnk

Other Details

This worm connects to the following possibly malicious URL:

  • {random IP addresses}

NOTES:

This worm modifies its file attributes to Read-only and Hidden after execution.

The auto-run registry, {random parameter 1} can be any of the following:

  • Network
  • Time
  • CrashReport
  • Database
  • Icon
  • Desktop
  • Tray
  • Video
  • Media

The auto-run registry, {random parameter 2} can be any of the following:

  • Checker
  • Informer
  • Notifyer
  • Saver
  • Updater
  • Verifyer

The dropped copy, {random file name} in removable drives can be any of the following:

  • click
  • game
  • hentai
  • installer
  • password
  • porn
  • run
  • sas
  • screensaver

It drops shortcut files pointing to the copy of itself in removable drives. These dropped .LNK files use the names of the folders located on the said drives for their file names. It then sets the attributes of the original folders to Hidden to trick the user into clicking the .LNK files.

It connects to random generated IP addresses with the following URL path:

  • /install.htm
  • /welcome.htm
  • /index.htm
  • /start.htm

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 10.490.02
FIRST VSAPI PATTERN DATE: 23 Dec 2013
VSAPI OPR PATTERN File: 10.491.00
VSAPI OPR PATTERN Date: 24 Dec 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

Scan your computer with your Trend Micro product and note files detected as WORM_KELIHOS.ALM

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • DefaultCompressedRecord = "{random value}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • RecordModifiedMax = "{random value}=="
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • FlagsModifiedValid = "0"
  • In HKEY_CURRENT_USER\Software\TansuTCP
    • ActiveModifiedTheme = "{random value}"
  • In HKEY_CURRENT_USER\Software\TansuTCP
    • SizeCompletedValid = "{random value}=="
  • In HKEY_CURRENT_USER\Software\TansuTCP
    • InfoPlayedCurrent = "0"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • {random parameter 1}{random parameter 2} = "{malware path and file name}"

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.
  • {Removable Drive Letter}:\{folder name}.lnk
  • {Removable Drive Letter}:\Shortcut to {random file name}.lnk

Step 6

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