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BKDR_KULUOZ.VH

January 15, 2013
 Analysis by: Mark Joseph Manahan
 ALIASES:

Win32/TrojanDownloader.Zortob.B trojan (Eset), TrojanDownloader:Win32/Kuluoz.B (Microsoft), Trojan.Fakeavlock (Symantec)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


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

It executes then deletes itself afterward.

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

  TECHNICAL DETAILS

File Size:

47,616 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

11 Jan 2013

Payload:

Connects to URLs/IPs, Compromises system security

Arrival Details

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

  • %Application Data%\{random}.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

It adds the following processes:

  • svchost.exe

It executes then deletes itself afterward.

It leaves the following text files:

  • {Malware Path and Filename}.txt

It injects codes into the following process(es):

  • created svchost.exe

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Sleep/Idle (2 minutes)
  • Download and execute arbitrary file
  • Update and uninstall itself
  • Visit URL

It connects to the following websites to send and receive information:

  • http://{BLOCKED}.{BLOCKED}.145.174:6667/{generated value}
  • http://{BLOCKED}.{BLOCKED}.10.68:8080/{generated value}
  • http://{BLOCKED}.{BLOCKED}.178.174:8080/{generated value}
  • http://{BLOCKED}.{BLOCKED}.224.202:8080/{generated value}
  • http://{BLOCKED}.{BLOCKED}.123.128:8080/{generated value}
  • http://{BLOCKED}.{BLOCKED}.203.178:8080/{generated value}
  • http://{BLOCKED}.{BLOCKED}.15:8080/{generated value}
  • http://{BLOCKED}.{BLOCKED}.135.154:8080/{generated value}

NOTES:

If the malware fails to connect to any of the C&C servers, it creates the following registries:

HKEY_CURRENT_USER\SOFTWARE\{random}

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run {random} = "%Application Data%\{random}.exe"

HKEY_CURRENT_USER\SOFTWARE\{random} {random} = "{hex values}"

The {generated value} is based on user name, Local IP, running debugger, and malware build date and version.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.656.05

FIRST VSAPI PATTERN DATE:

15 Oct 2012

VSAPI OPR PATTERN File:

9.657.00

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

Delete this registry key

[ 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
    • {random}

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
    • {random} = %Application Data%\{random}.exe

Step 5

Search and delete these components

[ Learn More ]
There may be some components 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.  
  • {Malware Path and Filename}.txt

Step 6

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