Analysis by: Michael Cabel
ALIASES:

W32/Autorun.worm.aaav (Mcafee); Worm:Win32/Autorun.WT (Microsoft); W32.SillyFDC (Symantec); Worm.Win32.AutoRun.hfp (Kaspersky)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This worm arrives via removable drives. It may be downloaded by other malware/grayware/spyware from remote sites. It may be unknowingly downloaded by a user while visiting malicious websites.

It modifies registry entries to hide files with System and Read-only attributes.

It drops copies of itself in all removable drives. 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

Arrival Details

This worm arrives via removable drives.

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

It may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This worm drops the following files:

  • %System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\bnf0342
  • %System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\info
  • %System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\wndsvc.dll

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

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

  • %System Root%\Program Files\Windows Alerter\WinAlert.exe
  • %System Root%\Program Files\Windows Common Files\Commgr.exe
  • %System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\WinSysApp.exe

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It creates the following folders:

  • %System Root%\Program Files
  • %System Root%\Program Files\Windows Alerter
  • %System Root%\Program Files\Windows Common Files
  • %System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

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
WindowMessenger = "%System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\WinSysApp.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Windows Alerter = "%System Root%\Program Files\Windows Alerter\WinAlert.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Windows Common Files Manager = "%System Root%\Program Files\Windows Common Files\Commgr.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
WindowMessenger = "%System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\WinSysApp.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Alerter = "%System Root%\Program Files\Windows Alerter\WinAlert.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Common Files Manager = "%System Root%\Program Files\Windows Common Files\Commgr.exe"

Other System Modifications

This worm modifies the following registry entries to hide files with System and Read-only attributes:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = 2

(Note: The default value data of the said registry entry is 1.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = 1

(Note: The default value data of the said registry entry is 0.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = 0

(Note: The default value data of the said registry entry is 1.)

Propagation

This worm drops copies of itself in all removable drives.

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\LaOiCaT.exe
Explore=RECYCLER\LaOiCaT.exe
AutoPlay=RECYCLER\LaOiCaT.exe
shell\Open\Command=RECYCLER\LaOiCaT.exe
shell\Open\Default=1
shell\Explore\command=RECYCLER\LaOiCaT.exe
shell\Autoplay\Command=RECYCLER\LaOiCaT.exe

Other Details

This worm does the following:

  • Searches for folders in all removable drives and drops a copy of itself using the name of the folders found as the file name of its dropped copies.

  SOLUTION

Minimum Scan Engine: 8.900

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

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
    • WindowMessenger = %System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\WinSysApp.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Windows Alerter = %System Root%\Program  Files\Windows Alerter\WinAlert.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Windows Common Files Manager = %System Root%\Program  Files\Windows Common Files\Commgr.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • WindowMessenger = %System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003\WinSysApp.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Windows Alerter = %System Root%\Program  Files\Windows Alerter\WinAlert.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Windows Common Files Manager = %System Root%\Program  Files\Windows Common Files\Commgr.exe

Step 4

Restore this modified 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\Explorer\Advanced
    • From: Hidden = 2
      To: 1
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: HideFileExt = 1
      To: 0
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
    • From: ShowSuperHidden = 0
      To: 1

Step 5

Search and delete AUTORUN.INF files created by WORM_AUTORUN.ZYG that contain these strings

[ Learn More ]
[Autorun]
Open=RECYCLER\LaOiCaT.exe
Explore=RECYCLER\LaOiCaT.exe
AutoPlay=RECYCLER\LaOiCaT.exe
shell\Open\Command=RECYCLER\LaOiCaT.exe
shell\Open\Default=1
shell\Explore\command=RECYCLER\LaOiCaT.exe
shell\Autoplay\Command=RECYCLER\LaOiCaT.exe

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. %System Root%\Program  Files
%System Root%\RECYCLER\X-1-5-21-1960408961-725345543-839522115-1003

Step 7

Scan your computer with your Trend Micro product to delete files detected as WORM_AUTORUN.ZYG. 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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