W32.Petch

SUMMARY

W32.Petch is a downloaded file that disables firewall and security software. This worm also deletes critical system files and changes the Internet Explorer home page to a pornographic page.

A Web site responsible for distributing this threat is no longer available.

This threat is UPX-packed and written in the Delphi programming language.

Virus definitions dated prior to October 31, 2003 may detect this threat as IRC.Trojan.Fgt.

Protection

• Virus Definitions (LiveUpdate™ Weekly) October 29, 2003
• Virus Definitions (Intelligent Updater) October 27, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Medium
• Threat Containment: Easy
• Removal: Difficult

Damage

• Damage Level: High
• Deletes Files: Deletes critical system files.
• Modifies Files: Changes the Internet Explorer home page.
• Causes System Instability: Removes critical registry keys.
• Compromises Security Settings: Terminates firewall and antivirus processes.

Distribution

• Distribution Level: Low
• Target of Infection: IRC users

TECHNICAL DETAILS

When W32.Petch runs, it performs the following actions:

1. Copies itself as:
   • C:WindowsSystem32Userinit32.exe
   • C:WindowsSystem32Dllhost32.exe
   • C:WindowsNotepad.exe
   • C:WindowsRegedit.exe
     
     

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     Note: These values are hard-coded and do not depend on system variables.

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2. Changes the value to:
   
   "Userinit"="C:Windowssystem32userinit32.exe"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon
   
   
3. Adds the value that refers to:
   
   C:Windowssystem32dllhost32.exe
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
   
4. Searches for and disables the following processes and programs:
   • _Avp32.exe
   • _avpcc.exe
   • _avpm.exe
   • Avnt.exe
   • Avp.exe
   • Blackice.exe
   • Blackice.exe
   • Ccevtmgr.exe
   • Ccsetmgr.exe
   • Fprot.exe
   • Fp-win.exe
   • Fsav32.exe
   • Fsgk32.exe
   • Fsm32.exe
   • Fsma32.exe
   • Fsma32.exe
   • Fsmb32.exe
   • Fsmb32.exe
   • Fssm32.exe
   • Fwenc.exe
   • Kavlite40eng.exe
   • Kavpers40eng.exe
   • N32scanw.exe
   • Nav auto-protect
   • Navapsvc.exe
   • Navapw32.exe
   • Navw32.exe
   • Nmain.exe
   • Normist.exe
   • Norton_internet_secu_3.0_407.exe
   • Npf40_tw_98_nt_me_2k.exe
   • Npfmessenger.exe
   • Nprotect.exe
   • Npssvc.exe
   • Nsched32.exe
   • Ntvdm.exe
   • Pavcl.exe
   • Pavsched.exe
   • Wfindv32.exe
   • Zapro.exe
   • Zapsetup3001.exe
   • Zatutor.exeZauinst.exe
   • Zonalm2601.exe
   • Zonealarm.exe
     
     
5. Deletes the following registry keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftInternet ExplorerDesktopSafeMode
   HKEY_LOCAL_MACHINESYSTEMControlSet001ControlSafeBoot
   HKEY_LOCAL_MACHINESYSTEMControlSet003ControlSafeBoot
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSafeBoot
   HKEY_LOCAL_MACHINESYSTEMMountedDevices
   HKEY_LOCAL_MACHINESYSTEMLastKnownGoodRecovery
   HKEY_LOCAL_MACHINESYSTEMControlSet001ControlContentIndexCatalogsSystem
   HKEY_LOCAL_MACHINESYSTEMControlSet001ControlBiosinfo
   
   
6. Resets the Internet Explorer home page by changing the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftInternet ExplorerMainStart Page
   
   to a value of www.blacksnake.com, which is a Web site that contains pornographic material.
   
   
7. Sets the default user name and the alternate default user name to C**K_S******G_F****T
   
   
8. Deletes the following files:
   • C: Windows System32Userinit.exe
   • C:WindowsCmd.exe
   • C:WindowsNotepad.exe
   • C:WindowsNotepad.exe
   • C:WindowsRegedit.exe
   • C:WindowsRegedit.exe
   • C:WindowsSystem32Alg.exe
   • C:WindowsSystem32Alg.exe
   • C:WindowsSystem32Autochk.exe
   • C:WindowsSystem32Autochk.exe
   • C:WindowsSystem32Bootok.exe
   • C:WindowsSystem32Bootok.exe
   • C:WindowsSystem32Chcp.exe
   • C:WindowsSystem32Chcp.exe
   • C:WindowsSystem32Chkdsk.exe
   • C:WindowsSystem32Chkntfs.exe
   • C:WindowsSystem32Chkntfs.exe
   • C:WindowsSystem32Ctfmon.exe
   • C:WindowsSystem32Ctfmon.exe
   • C:WindowsSystem32Dumprep.exe
   • C:WindowsSystem32Dumprep.exe
   • C:WindowsSystem32Imapi.exe
   • C:WindowsSystem32Imapi.exe
   • C:WindowsSystem32Logon.exe
   • C:WindowsSystem32Logon.exe
   • C:WindowsSystem32MDM.exe
   • C:WindowsSystem32MDM.exe
   • C:WindowsSystem32Ntkrnlpa.exe
   • C:WindowsSystem32Ntkrnlpa.exe
   • C:WindowsSystem32Ntoskrnl.exe
   • C:WindowsSystem32Ntoskrnl.exe
   • C:WindowsSystem32Progman.exe
   • C:WindowsSystem32Progman.exe
   • C:WindowsSystem32Recover.exe
   • C:WindowsSystem32Recover.exe
   • C:WindowsSystem32Regedt32.exe
   • C:WindowsSystem32Regsvr32.exe
   • C:WindowsSystem32Services.exe
   • C:WindowsSystem32Services.exe
   • C:WindowsSystem32Shutdown.exe
   • C:WindowsSystem32Shutdown.exe
   • C:WindowsSystem32Systray.exe
   • C:WindowsSystem32Systray.exe
   • C:WindowsSystem32Taskman.exe
   • C:WindowsSystem32Taskmgr.exe
   • C:WINDOWSSystem32Userinit.exe
   • C:WindowsSystem32Win.exe
   • C:WindowsSystem32Win.exe
   • C:WindowsSystem32Wowexec.exe
   • C:WindowsSystem32Wowexec.exe
   • C:WindowsSystem32Wuauclt.exe
   • C:WindowsSystem32Wuauclt.exe
   • C:WindowsTASKMAN.exe
     
     

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     Note: These paths are hard-coded and do not depend on system variables. If the worm deletes these files, in most cases, Windows will no longer run when the computer is restarted.

     ---

     
     
9. Removes most, if not all, of the subkey paths from the following registry subkeys of HKEY_LOCAL_MACHINE:
   
   HARDWARE
   SECURITY
   SOFTWARE
   SYSTEM
   Software
   System
   
   
10. Displays the fake error message:
    
    Error in memory block: #A5487F
    
    
11. Runs mIRC and executes a one-line command with the message "...//************/britney.jpg <- uuh, check it out !! :D"
    
    If ActiveX controls are enabled when the file is downloaded, it will execute. Since firewall protection is disabled, there is no other warning about ActiveX applications.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

REMOVAL

These removal instructions will work if W32.Petch has not yet been executed.

If W32.Petch has already been executed, it is likely that you will no longer be able to start Windows. While the damage that W32.Petch does varies with the installation path, once it runs, it makes numerous changes to the registry and deletes system files.

In this situation, replace the deleted files and the Windows registry either from a clean backup, or re-install the operating system.

Once you have replaced the registry with a clean copy and have restored any missing system files, update the virus definitions and run a full system scan as described in the next section.

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Run a full system scan and delete all the files detected as W32.Petch.

For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

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Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

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For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan all files."
2. Run a full system scan.
3. If any files are detected as infected with W32.Petch, click Delete.