Analysis by: Anthony Joe Melgarejo
ALIASES:

TrojanDownloader:Win32/Kuluoz (Microsoft), Trojan.Win32.Kuluoz.b (v) (VIPRE), W32/Dofoil.AO!tr (Fortinet)

 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:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users. It 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: 40,960 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 17 Jun 2013

Arrival Details

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

It 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 files:

  • {initial malware copy's directory}\{initinial malware file name}.txt

It drops the following copies of itself into the affected system:

  • %AppDataLocal%\{random}.exe

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

Autostart Technique

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

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

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\SOFTWARE\{random}

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

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

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://{BLOCKED}.131.225:8080/{generated value}
  • http://{BLOCKED}.47.151:8080/{generated value}
  • http://{BLOCKED}.208.180:8090/{generated value}
  • http://{BLOCKED}.139.235:8080/{generated value}
  • http://{BLOCKED}.5.102:8080/{generated value}
  • http://{BLOCKED}.6.40:8080/{generated value}
  • http://{BLOCKED}.12.83:8080/{generated value}
  • http://{BLOCKED}.132.29:8080/{generated value}
  • http://{BLOCKED}.226.51:8080/{generated value}
  • http://{BLOCKED}.253.250:8080/{generated value}
  • http://{BLOCKED}.226.241:8080/{generated value}

    It opens the following files:

    • {initial malware copy's directory}\{initinial malware file name}.txt

  SOLUTION

Minimum Scan Engine: 9.300

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 BKDR_KULUOZ.QWJ

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

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 5

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} = %AppDataLocal%\{random}.exe

Step 6

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.
  • {initial malware copy's directory}\{initinial malware file name}.txt

Step 7

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