TROJ_DLOADER.JWK

October 09, 2012
 Analysis by: Mark Joseph Manahan
 ALIASES:

TrojanDownloader:Win32/Dofoil.R (Microsoft), Trojan-PSW.Win32.Tepfer.apmf (Kaspersky), PWS-Zbot.gen.ahr (McAfee)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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.

It executes then deletes itself afterward.

  TECHNICAL DETAILS

File Size:

195,073 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

24 Jul 2012

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 and executes them:

  • %User Profile%\Application Data\{6 Random Hex Number}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It executes then deletes itself afterward.

Autostart Technique

This Trojan creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Explorer\Run
{Random Software Name} = "%User Profile%\Application Data\{6 Random Hex Number}.exe"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}2.org/images/index.php

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

9.284.01

FIRST VSAPI PATTERN DATE:

25 Jul 2012

VSAPI OPR PATTERN File:

9.285.00

VSAPI OPR PATTERN Date:

26 Jul 2012

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

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\Policies\Explorer\Run
    • {Random Software Name} = "%User Profile%\Application Data\{6 Random Hex Number}.exe"

Step 4

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