WORM_DELF.IOF

April 07, 2014
 Modified by: Rika Joi Gregorio
 ALIASES:

Worm:Win32/Delf(Microsoft), Win32/AutoRun.Delf.DM worm(Eset), Worm.Win32.Delf(Ikarus)

 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:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This worm arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size:

20,992 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

06 Oct 2011

Arrival Details

This worm 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 copies of itself into the affected system and executes them:

  • %System%\kb{random digit}.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

It drops the following files:

  • {Drive Letter}:\RECYCLER\RECYCLER\desktop.ini
  • %System%\usbmons.dll

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

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

  • %System%\usbmons.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

Other System Modifications

This worm adds the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
Notify\usbmon

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
Notify\usbmon
DLLName = "%System%\usbmons.dll"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
Notify\usbmon
Shutdown = "DoShutdown"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
Notify\usbmon
Startup = "DoStartup"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
Notify\usbmon
Asynchronous = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\
Notify\usbmon
Impersonate = "0"

Propagation

This worm creates the following folders in all removable drives:

  • {Drive Letter}:\RECYCLER
  • {Drive Letter}:\RECYCLER\RECYCLER

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

  • {Drive Letter}:\RECYCLER\RECYCLER\autorun.exe

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[autorun]
open=.\RECYCLER\RECYCLER\autorun.exe

shell\1=Open
shell\1\Command=.\RECYCLER\RECYCLER\autorun.exe
shell\2=Browser
shell\2\Command=.\RECYCLER\RECYCLER\autorun.exe

shellexecute=.\RECYCLER\RECYCLER\autorun.exe

Other Details

This worm connects to the following possibly malicious URL:

  • http://{BLOCKED}.{BLOCKED}.94.218/_vti_cnf/help11.gif

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.880.08

FIRST VSAPI PATTERN DATE:

26 Apr 2013

VSAPI OPR PATTERN File:

9.881.00

VSAPI OPR PATTERN Date:

27 Apr 2013

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 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.

 
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify
    • usbmon

Step 4

Search and delete this folder

[ 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.
  • {Drive Letter}:\RECYCLER

Step 5

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.
  • {Drive Letter}:\RECYCLER\RECYCLER\desktop.ini
  • %System%\usbmons.dll

Step 6

Search and delete AUTORUN.INF files created by WORM_DELF.IOF that contain these strings

[ Learn More ]


[autorun]
open=.\RECYCLER\RECYCLER\autorun.exe

shell\1=Open
shell\1\Command=.\RECYCLER\RECYCLER\autorun.exe
shell\2=Browser
shell\2\Command=.\RECYCLER\RECYCLER\autorun.exe

shellexecute=.\RECYCLER\RECYCLER\autorun.exe

Step 7

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