Threat Descriptions

Dumaru.Z

Classification

Category :

Malware

Type :

Worm

Platform :

W32

Aliases :

Dumaru.Z, W32.Dumaru.Z@mm

Summary

A new variant of the Dumaru worm family has been found in the wild on 25th of January, 2004.

This variant of the worm is really similar to the Y variant with the following differences:

  • The FTP backdoor has been removed
  • The TCP bouncer proxy has been removed
  • The code has been reorganized internally
  • This variant downloads a trojan which is detected as TrojanDropper.Win32.Small.aw by F-Secure Anti-Virus

Removal

Dumaru.Z can be removed manually by performing the following steps:

  • 1, Delete the registry value:
    • HKLM\Software\Microsoft\Windows\CurrentVersion\Run\load32
  • 2, Delete the files:
    • %SysDir%\l32x.exe
    • %SysDir%\vxd32v.exe
    • dllxw.exe
      • from the Starup Directory
  • 3, Restore 'system.ini' to 
     [Boot]
Shell=explorer
  • 4, Restart the computer

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

Technical Details

System Infection

Upon execution Dumaru.Z installs several copies of itself to the computer:

  • 'l32x.exe' to the Windows System Directory which is added to the registry as 
     HKLM\Software\Microsoft\Windows\CurrentVersion\Run\load32
  • 'dllxw.exe' is copied to the current users' Startup Directory.
  • 'vxd32v.exe' to the Windows System Directory which is added to the system.ini: 
     [Boot]
Shell=explorer vxd32v.exe

Email Propagation

Dumaru.Z uses its own SMTP engine to send emails. The SMTP engine performs a direct name service lookup on the target domain so it does not depend on the infected computer's email server settings.

To collect email addresses the worm recursively searches through all the directories on the computer and looks for files that could contain email addresses: 

'.htm'
'.wab'
'.html
'.dbx'
'.tbb'
'.abd'

Going through the list of collected addresses Dumaru.Z sends emails with infected attachments that have to following characteristics: 

From: "Elene" [F*CKENSUICIDE@HOTMAIL.COM] To: [user@targeted.somewhere] Subject: Important information for you. Read it immediately ! Body: Here is my photo, that you asked for yesterday. Attachment: myphoto.zip

Payloads

Dumaru.Z - just like it's earlier variants - comes with capabilities to steal sensitive user data:

  • user's POP3 password
  • clipboard data
  • Protected Storage Data
  • User credentials and key log data of visits to www.e-gold.com

The collected data is sent to a predefined email address.

Trojan Downloader

Dumaru.Z has a function that downloads a trojan from a predefined location and places it to 'nvidia32.exe' to the Windows Directory.

The downloaded file is then executed to activate the trojan.