W32.Petch.B

SUMMARY

The W32.Petch.B Trojan horse is a variant of W32.Petch that spreads by downloading an infected file through IRC. It deletes critical files, disables recovery settings, and changes the Internet Explorer start page.

The Trojan is written in Delphi and is packed with UPX.

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 5, 2003
• Virus Definitions (Intelligent Updater) November 3, 2003

Threat Assessment

Wild

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

Damage

• Damage Level: High
• Deletes Files: Deletes critical system files.
• Modifies Files: Modifies the system registry.
• Causes System Instability: Removes safe recovery for Windows NT systems.

Distribution

• Distribution Level: Low
• Target of Infection: mIRC channels in a users configuration files.

TECHNICAL DETAILS

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

1. Deletes the following critical system files:
   
   • %windir%egedit.exe
   • %windir%system32 askman.exe
   • %windir%system32 askmgr.exe
   • %windir%system32egedt32.exe
   • %windir%system32egsvr32.exe
   • %windir%TASKMAN.exe
   • C:Windowssystem32userinit.exe
     
     

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     Note: %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to that location.

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2. Copies itself as:
   
   • %windir%system32userinit32.exe
   • %windir%system32ctfmon32.exe
   • %windir%system32autochk.exe
   • %windir%system32chkntfs.exe
   • %windir%system32chkdsk.exe
   • %windir%system32ecover.exe
   • %windir%NOTEPAD.exe
   • %windir%egedit.exe
     
     
3. Changes the value:
   
   "Userinit" = "%windir%system32userinit.exe"
   
   to:
   
   "Userinit" = "%windir%system32userinit32.exe"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon
   
   so that the Trojan starts when Windows NT/2000/XP starts.
   
   
4. Adds the value:
   
   "SCRNSAVE.EXE" = "%windir%system32ctfmon32.exe"
   
   to the registry key:
   
   HKEY_CURRENT_USERControl PanelDesktop
   
   to ensure that the Trojan runs if a screen saver is configured.
   
   
5. Resets or deletes the following registry keys (Windows NT/2000/XP only):
   
   • HKEY_CURRENT_USERSoftwareMicrosoftInternet ExplorerDesktopSafeMode
   • HKEY_LOCAL_MACHINESYSTEMControlSet001ControlSafeBoot
   • HKEY_LOCAL_MACHINESYSTEMControlSet003ControlSafeBoot
   • HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSafeBoot
   • HKEY_LOCAL_MACHINESYSTEMControlSet001ControlContentIndex
     CatalogsSystem
   • HKEY_LOCAL_MACHINESYSTEMControlSet001ControlBiosinfo
   • HKEY_LOCAL_MACHINESYSTEMMountedDevices
   • HKEY_LOCAL_MACHINESYSTEMLastKnownGoodRecovery
     
     which removes access to a variety of options, such as the ability to boot to Safe Mode, and the Last Known Good Configuration feature.
     
     
6. Modifies the value:
   
   "Start Page"="www.blacksnake.com"
   
   in the registry key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftInternet ExplorerMain
   
   which changes the Internet Explorer Home page.
   
   
7. Opens mIRC and runs a one line script to send a message that reads:
   
   www.angelfire.com/pro/pics33/jessica_alba.jpg <- wow !!
   
   

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   Note: This file contains the Trojan.

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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

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.B.
4. Delete the value that was added to the registry.
5. Restore the Internet Explorer settings.
   

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

1. To disable 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 you are satisfied that the threat has been removed, you should 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. To update 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. To scan for and delete 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.B, click Delete.

4. To delete the value from the registry

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WARNING: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

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1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon
   
   
4. In the right pane, double-click:
   
   Userinit
   
   
5. In the Value data box, change the last part of the text from:
   
   userinit32.exe
   
   to:
   
   userinit.exe
   
   and click OK.
   
   
6. Navigate to the key:
   
   HKEY_CURRENT_USERControl PanelDesktop
   
   
7. In the right pane, delete the value:
   
   "SCRNSAVE.EXE" = "%windir%system32ctfmon32.exe"
   
   
8. Exit the Registry Editor.
   
   

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   Note: Given the particularly destructive nature of this Trojan, Symantec recommends restoring the registry from a clean backup to restore the functionality of the various Windows features that the virus disables in step 5 of the "Technical Details" section.

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5. To restore the Internet Explorer settings
Some of the changes that the Trojan makes to the registry will modify some Internet Explorer settings. One of the settings that it changes is to the home page.

To reset the home page:

1. Start Microsoft Internet Explorer.
2. Connect to the Internet and go to the page that you want to set as your home page.
3. Click Tools, and then click Internet Options.
4. In the Home page section of the General tab, click Use Current, and then click OK.

If you notice any other problems when using Internet Explorer, change these settings within the program. See your Internet Explorer documentation for instructions.