WORM_DELF.SK

 Modified by: Jaime Benigno Reyes

 ALIASES:

Trojan horse Delf.AMET.dropper (AVG), a variant of Win32/Delf.OKK trojan (Nod32)

 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:
 INFORMATION EXPOSURE:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Propagates via removable drives


This worm arrives by connecting affected removable drives to a system. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size:

Varies

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

30 Jan 2014

Payload:

Collects system information, Connects to URLs/IPs

Arrival Details

This worm arrives by connecting affected removable drives to a system.

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 worm drops the following component file(s):

  • %Application Data%\{folder name}\{filename 2} (also detected as WORM_DELF.SK)
  • %Windows%\Tasks\GoogleUpdateTaskUserS-17769-185731846-2809907627-500Core.job (scheduled task)

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

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

  • %Application Data%\{folder name}\{filename 1}

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

It uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.

It creates the following folders:

  • %Application Data%\{folder name}

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

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
GuardMailRu = "%Application Data%\{folder name}\{filename 1}"

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Taskman = "%Application Data%\{folder name}\{filename 1}"

The scheduled task executes the malware every:

  • minute

Other System Modifications

This worm adds the following registry entries:

HKEY_CURRENT_USER\Console
fileagain = "filename 1"

HKEY_CURRENT_USER\Console
lib = "filename 2"

HKEY_CURRENT_USER\Console
windir = "folder name"

Propagation

This worm drops the following copy(ies) of itself in all removable drives:

  • {removable drive letter}:\Ëè÷íîå.pif

Backdoor Routine

This worm executes the following commands from a remote malicious user:

  • download arbitrary files
  • perform remote shell commands
  • get system information

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • http://{BLOCKED}ol.ru

Information Theft

This worm gathers the following data:

  • user name
  • drive information
  • OS version

NOTES:

filename 1 could be one of the following:

  • svshost.com
  • svshost.exe
  • adwans.exe
  • smmsr.exe
  • mms.exe
  • taskhosts.exe
  • winrars.exe
  • msi.exe
  • conhos.exe
  • conime.exe
  • bfsvc.exe

filename 2 could be one of the following:

  • desktop.ini
  • boot.ini
  • tmp.tmp
  • win.ini
  • setup.log
  • vclx70.bpl
  • win32k.bad
  • impact.ksr
  • attribyt.lib
  • cool.txt
  • parabellym.inf

folder name could be one of the following:

  • temp
  • java
  • Boot
  • assembly
  • AppPatch
  • Help
  • Media
  • Setup
  • ru-RU
  • winsxs
  • migration

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

10.574.03

FIRST VSAPI PATTERN DATE:

30 Jan 2014

VSAPI OPR PATTERN File:

10.575.00

VSAPI OPR PATTERN Date:

31 Jan 2014

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

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\Run
    • GuardMailRu = "%Application Data%\{folder name}\{filename 1}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
    • Taskman = "%Application Data%\{folder name}\{filename 1}"
  • In HKEY_CURRENT_USER\Console
    • fileagain = "filename 1"
  • In HKEY_CURRENT_USER\Console
    • lib = "filename 2"
  • In HKEY_CURRENT_USER\Console
    • windir = "folder name"

Step 4

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.
  • %Windows%\Tasks\GoogleUpdateTaskUserS-17769-185731846-2809907627-500Core.job

Step 5

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Application Data%\{folder name}

Step 6

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