Analysis by: kathleenno
ALIASES:

Trojan-Dropper.Win32.Dapato.ew (Kaspersky); Troj/Dloadr-DHZ (Sophos); TrojanDownloader.Small.peb (Vba32)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This Trojan drops a non-malicious .PDF file in its current directory as {FILE NAME}.PDF and opens the said file to hide its execution.

It parses the content from certain URLs. Depending on the content, it may download a file and save it in %Windows%. It then executes the said file. However, as of this writing the said URL contains no data.

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 deletes registry entries, causing some applications and programs to not function properly.

It executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 482,816 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 18 Jul 2011
Payload: Connects to URLs/IPs, Drops files

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.

This malware arrives via the following means:

  • Arrives as the following file:
    • {FILE NAME}.PDF.EXE

Installation

This Trojan drops the following files:

  • %Application Data%\Microsoft\update.exe - also detected as TROJ_DLOADR.ZTZ

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

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
SysUpdate = "%Application Data%\Microsoft\update.exe"

Other System Modifications

This Trojan deletes the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
SysTray =

Dropping Routine

This Trojan executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}ly.{BLOCKED}linesite.com/index.html

It deletes itself after execution.

NOTES:

It drops a non-malicious .PDF file in its current directory as {FILE NAME}.PDF and opens the said file to hide its execution.

It parses the content from the abovementioned URL. Depending on the content, it may download a file and save it in %Windows%. It then executes the said file. However, as of this writing the said URL contains no data.

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 8.296.10
FIRST VSAPI PATTERN DATE: 18 Jul 2011

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

Identify and terminate files detected as TROJ_DLOADR.ZTZ

[ Learn More ]
  1. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  2. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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\Run
    • SysUpdate = %Application Data%\Microsoft\update.exe

Step 4

Search and delete these files

[ Learn More ]
There may be some component 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.
  • {FILE NAME}.PDF

Step 5

Scan your computer with your Trend Micro product to delete files detected as TROJ_DLOADR.ZTZ. 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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