Analysis by: Sabrina Lei Sioting
 Modified by: Sabrina Sioting
 PLATFORM:

Windows 2000, Windows XP, Windows 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 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: 49,152 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 06 Mar 2009

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 copies of itself into the affected system:

  • %Windows%\Downloaded Program Files\CxUSBKey.exe

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

It drops the following component file(s):

  • %System%\AceExt32.dll - detected as the same malware

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Its DLL component is injected to the following process(es):

  • EXPLORER.EXE

Autostart Technique

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

HKEY_CLASSES_ROOT\CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}\
InprocServer32
{Default} = "%System%\AceExt32.dll"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}\InprocServer32
{Default} = "%System%\AceExt32.dll"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\ShellServiceObjectDelayLoad
AceExt = "{35CEC8A3-2BE6-11D2-8773-92E220524150}"

Other System Modifications

This worm adds the following registry entries as part of its installation routine:

HKEY_CLASSES_ROOT\CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}
{Default} = "AceExt"

HKEY_CLASSES_ROOT\CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}\
InprocServer32
ThreadingModel = "Both"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}
{Default} = "AceExt"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}\InprocServer32
ThreadingModel = "Both"

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

HKEY_CLASSES_ROOT\CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}

HKEY_CLASSES_ROOT\CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}\
InprocServer32

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{35CEC8A3-2BE6-11D2-8773-92E220524150}\InprocServer32

Propagation

This worm creates the following folders in all removable drives:

  • RECYCLER

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

  • RECYCLER\UcHelp.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]
Shell=´ò¿ª(&O)
shell\´ò¿ª(&O)\command=RECYCLER\UcHelp.exe

Dropping Routine

This worm sets the attributes of its dropped file(s) to the following:

  • Hidden
  • System

NOTES:

The dropped AUTORUN.INF is detected by Trend Micro as Mal_Otorun1.

It drops the following component file(s) in all removable drives:

  • RECYCLER\desktop.ini

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 5.883.00
FIRST VSAPI PATTERN DATE: 06 Mar 2009

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

Remove malware files dropped/downloaded by WORM_AGENT.USS

     Mal_Otorun1

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\CLSID\
    • {35CEC8A3-2BE6-11D2-8773-92E220524150}
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\
    • {35CEC8A3-2BE6-11D2-8773-92E220524150}

Step 5

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\ShellServiceObjectDelayLoad
    • AceExt = {35CEC8A3-2BE6-11D2-8773-92E220524150}

Step 6

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.
  • %Drive letter%\RECYCLER

Step 7

Search and delete AUTORUN.INF files created by WORM_AGENT.USS that contain these strings

[ Learn More ]


[AutoRun]
Shell=´ò¿ª(&O)
shell\´ò¿ª(&O)\command=RECYCLER\UcHelp.exe

Step 8

Scan your computer with your Trend Micro product to delete files detected as WORM_AGENT.USS. 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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