WORM_SILLY.CT

 Analysis by: JessaD
 Modified by: Christopher Daniel So

 ALIASES:

W32.SillyFDC (Symantec), Mal/DownLdr-AK (Sophos), Worm.Win32.AutoRun (Sunbelt), W32/Metacrypt.9 (Fortinet), TR/Downloader.Gen (AntiVir)

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW


This worm arrives by connecting affected removable drives to a system. It may be downloaded by other malware/grayware/spyware from remote sites. It may be dropped by other malware.

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:

53,248 bytes

File Type:

PE

Memory Resident:

Yes

Initial Samples Received Date:

11 Jan 2011

Arrival Details

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

It may be downloaded by other malware/grayware/spyware from remote sites.

It may be dropped by other malware.

Installation

This worm drops the following copies of itself into the affected system:

  • %Windows%\igfxsrvc.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

  • 190ajloxcnhw09u09hqoi;3w4oi4oih2oi

Autostart Technique

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

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
lgxfsrvc = "%Windows%\igfxsrvc.exe"

Propagation

This worm creates the following folders in all removable drives:

  • {removable drive}:\RECYCLER\S-1-5-21-3441485041-918478196-174860263-1004

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

  • {removable drive}:\RECYCLER\S-1-5-21-3441485041-918478196-174860263-1004\RUN.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\S-1-5-21-3441485041-918478196-174860263-1004\run.exe
icon=%SystemRoot%\system32\SHELL32.dll,4
action=Open folders to view files
shell\open=1
shell\open\command=.\RECYCLER\S-1-5-21-3441485041-918478196-174860263-1004\run.exe
shell\open\default=1

Other Details

This worm does the following:

  • It searches for all PPT files in the system. It then connects to http://115.145.229.85/naver.php?naver={PPT file name}.

NOTES:
As of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

8.900

VSAPI PATTERN File:

7.760.07

VSAPI PATTERN Date:

13 Jan 2011

VSAPI PATTERN Date:

1/13/2011 12:00:00 AM

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 WORM_SILLY.CT

[ 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_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • lgxfsrvc=%Windows%\igfxsrvc.exe

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. {removable drive}:\RECYCLER\S-1-5-21-3441485041-918478196-174860263-1004

Step 5

Search and delete AUTORUN.INF files created by WORM_SILLY.CT that contain these strings

[ Learn More ]
[autorun]
open=.\RECYCLER\S-1-5-21-3441485041-918478196-174860263-1004\run.exe
icon=%SystemRoot%\system32\SHELL32.dll,4
action=Open folders to view files
shell\open=1
shell\open\command=.\RECYCLER\S-1-5-21-3441485041-918478196-174860263-1004\run.exe
shell\open\default=1

Step 6

Scan your computer with your Trend Micro product to delete files detected as WORM_SILLY.CT. 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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