TROJ_DLDR.FX

October 08, 2012
 Analysis by: jasperm
 PLATFORM:

Windows 2000, XP, 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 may be dropped by other malware. It may be unknowingly downloaded by a user while visiting malicious websites. However, as of this writing, the said sites are inaccessible.

It executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  TECHNICAL DETAILS

File Size:

32,768 bytes

File Type:

PE

Memory Resident:

Yes

Initial Samples Received Date:

29 Oct 2010

Payload:

Connects to URLs/Ips, Downloads files

Arrival Details

This Trojan may be dropped by other malware.

It may be unknowingly downloaded by a user while visiting malicious websites.

However, as of this writing, the said sites are inaccessible.

Installation

This Trojan is injected into the following processes running in memory:

  • EXPLORER.EXE

Autostart Technique

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

HKEY_CLASSES_ROOT\CLSID\{1A7882DB-B89E-4406-AF8A-42C3DBD11B2C}\
InprocServer32
@ = {malware path and file name]

Other System Modifications

This Trojan adds the following registry keys as part of its installation routine:

HKEY_CLASSES_ROOT\Comhtml.mshtml

HKEY_CLASSES_ROOT\Comhtml.mshtml.1

HKEY_CLASSES_ROOT\CLSID\{1A7882DB-B89E-4406-AF8A-42C3DBD11B2C}

HKEY_CLASSES_ROOT\TypeLib\{B02DAAF7-C679-4D00-9805-BE94D23B3B99}

Download Routine

This Trojan then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

Other Details

Based on analysis of the codes, it has the following capabilities:

  • Upon execution, it gets the local time and connects to the website, http://{BLOCKED}e.idirectech.com/support.html when the day is Thursday and the time is above 9 AM (10 AM - 11 PM).
  • Based on its code, the reply from the server is a script which contains strings. It then matches the strings to its list of strings to check the file to download.

  SOLUTION

Minimum Scan Engine:

8.900

VSAPI PATTERN File:

under testing

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

Scan your computer with your Trend Micro product and note files detected as TROJ_DLDR.FX

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

 
  • In HKEY_CLASSES_ROOT
    • Comhtml.mshtml
  • In HKEY_CLASSES_ROOT
    • Comhtml.mshtml.1  
  • In HKEY_CLASSES_ROOT\CLSID
    • {1A7882DB-B89E-4406-AF8A-42C3DBD11B2C}
  • In HKEY_CLASSES_ROOT\TypeLib
    • {B02DAAF7-C679-4D00-9805-BE94D23B3B99} 

Step 5

Search and delete the file detected as TROJ_DLDR.FX

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files in the search result.

Step 6

Scan your computer with your Trend Micro product to delete files detected as TROJ_DLDR.FX. 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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