W32.Zotob.B

SUMMARY

W32.Zotob.B is a worm that spreads by exploiting Microsoft Windows Plug and Play Buffer Overflow Vulnerability (described in Microsoft Security Bulletin MS05-039)

Note:

• Virus definitions version 70814p (extended version 8/14/2005 rev. 16) or higher are required to detect this risk.
• While computers running Windows 95/98/Me/NT4/XP operating systems cannot be infected remotely, it is possible they could be infected if W32.Zotob.B is executed locally (although this is an unlikely occurrence). Vulnerable Windows 2000 computers could then be infected by the compromised computer.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 14, 2005
• Virus Definitions (Intelligent Updater) August 14, 2005

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Payload: Allows unauthorized remote access.

Distribution

• Distribution Level: Medium
• Ports: TCP ports 445, 8080, and 33333.
• Target of Infection: Targets systems which can be exploited by the Microsoft Windows Plug and Play Service Vulnerability (MS05-039).

TECHNICAL DETAILS

When W32.Zotob.B is executed, it performs the following actions:

1. Creates the following mutex so that only one copy of the worm runs on the compromised computer:
   
   B-O-T-Z-O-R
   
   
2. Copies itself as %System%csm.exe.
   
   Note: %System% is a variable that refers to the System folder. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   
   
3. Adds the value:
   
   "csm Win Updates" = "csm.exe"
   
   to the registry subkeys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   RunServices
   
   so that it runs every time Windows starts.
   
   
4. Modifies the value:
   
   "Start" = "4"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesSharedAccess
   
   to disable the Shared Access service in Windows 2000/XP.
   
   
5. Connects to an IRC server on the domain [http://]wait.atillaekici.net[REMOVED] on TCP port 8080. This allows unauthorized remote access to the compromised computer.
   
   
6. Opens an FTP server on TCP port 33333.
   
   
7. Generates random IP address from the current IP address. The worm does this by keeping the first two octets of the IP address on the system and randomize the last two octets. For example, if the IP address of the system is 192.168.0.1, the worm will attempt to infect IP addresses beginning with 192.168.x.x.
   
   
8. Attempts to spread to computers with the above random IP address by opening a backdoor using TCP port 8888 on the remote computer. The worm does this by attempting to exploit the Microsoft Windows Plug and Play Buffer Overflow Vulnerability (described in Microsoft Security Bulletin MS05-039)
   
   
9. Copies the following file to the newly compromised computer and executes an FTP script contained within it:
   
   %System%2pac.txt
   
   
10. Downloads and executes the following copy of the worm from the previously created FTP server on the host computer:
    
    %System%haha.exe
    
    
11. Adds the following entries to the hosts file:
    
    .... Made By .... Greetz to good friend  [REMOVED]  in the next 24hours!!!

n127.0.0.1 www.symantec.com
127.0.0.1 securityresponse.symantec.com
127.0.0.1 symantec.com
127.0.0.1 www.sophos.com
127.0.0.1 sophos.com
127.0.0.1 www.mcafee.com
127.0.0.1 mcafee.com
127.0.0.1 liveupdate.symantecliveupdate.com
127.0.0.1 www.viruslist.com
127.0.0.1 viruslist.com
127.0.0.1 viruslist.com
127.0.0.1 f-secure.com
127.0.0.1 www.f-secure.com
127.0.0.1 kaspersky.com
127.0.0.1 kaspersky-labs.com
127.0.0.1 www.avp.com
127.0.0.1 www.kaspersky.com
127.0.0.1 avp.com
127.0.0.1 www.networkassociates.com
127.0.0.1 networkassociates.com
127.0.0.1 www.ca.com
127.0.0.1 ca.com
127.0.0.1 mast.mcafee.com
127.0.0.1 my-etrust.com
127.0.0.1 www.my-etrust.com
127.0.0.1 download.mcafee.com
127.0.0.1 dispatch.mcafee.com
127.0.0.1 secure.nai.com
127.0.0.1 nai.com
127.0.0.1 www.nai.com
127.0.0.1 update.symantec.com
127.0.0.1 updates.symantec.com
127.0.0.1 us.mcafee.com
127.0.0.1 liveupdate.symantec.com
127.0.0.1 customer.symantec.com
127.0.0.1 rads.mcafee.com
127.0.0.1 trendmicro.com
127.0.0.1 pandasoftware.com
127.0.0.1 www.pandasoftware.com
127.0.0.1 www.trendmicro.com
127.0.0.1 www.grisoft.com
127.0.0.1 www.microsoft.com
127.0.0.1 microsoft.com
127.0.0.1 www.virustotal.com
127.0.0.1 virustotal.com
127.0.0.1 www.amazon.com
127.0.0.1 www.amazon.co.uk
127.0.0.1 www.amazon.ca
127.0.0.1 www.amazon.fr
127.0.0.1 www.paypal.com
127.0.0.1 paypal.com
127.0.0.1 moneybookers.com
127.0.0.1 www.moneybookers.com
127.0.0.1 www.ebay.com
127.0.0.1 ebay.com

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

Removal using the W32.Zotob Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of W32.Zotob.B. Use this removal tool first, as it is the easiest way to remove this threat.

Manual 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. Remove all the entries that the risk added to the hosts file
3. Update the virus definitions.
4. Run a full system scan and delete all the files detected.
5. Delete any values added to the registry.
6. Reenable the SharedAccess service (Windows 2000/XP only).
   

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

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

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 remove all the entries that the risk added to the hosts file

1. Navigate to the following location:
   
   
   • Windows 95/98/Me:
     %Windir%
   • Windows NT/2000/XP:
     %Windir%System32driversetc
     
     Notes:
   • The location of the hosts file may vary and some computers may not have this file. There may also be multiple copies of this file in different locations. If the file is not located in these folders, search your disk drives for the hosts file, and then complete the following steps for each instance found.
   • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows (Windows 95/98/Me/XP) or C:Winnt (Windows NT/2000).
     
     
2. Double-click the hosts file.
3. If necessary, deselect the "Always use this program to open this program" check box.
4. Scroll through the list of programs and double-click Notepad.
5. When the file opens, delete all the entries added by the risk. (See the Technical Details section for a complete list of entries.)
6. Close Notepad and save your changes when prompted.
   

3. 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 Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. 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 Virus Definitions (Intelligent Updater).
  
  The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions. For detailed instructions read the document: How to update virus definition files using the Intelligent Updater.

4. 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, click Delete.

Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.

After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [FILE PATH]
Message body: Windows cannot find [FILE NAME]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.


5. To delete the value from the registry
Important: 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 subkeys only. For instructions refer to the document: How to make a backup of the Windows registry.

1. Click Start > Run.
2. Type regedit
3. Click OK.
   
   Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.
   
   
4. Navigate to the subkeys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersion
   RunServices
   
   
5. In the right pane, delete the value:
   
   "csm Win Updates" = "csm.exe"
   
   
6. Exit the Registry Editor.

6. To reenable the SharedAccess service (Windows 2000/XP only)
The SharedAccess service is responsible for maintaining Internet Connection Sharing and the Windows Firewall/Internet Connection Firewall applications in Windows. (The presence and names of these applications vary depending on the operating system and service pack you are using.) To protect your computer and maintain network functionality, re-enable this service if you are using any of these programs.


Windows XP Service Pack 2
If you are running Windows XP with Service Pack 2 and are using the Windows Firewall, the operating system will alert you when the SharedAccess service is stopped, by displaying an alert balloon saying that your Firewall status is unknown. Perform the following steps to ensure that the Windows Firewall is re-enabled:

1. Click Start > Control Panel.
   
   
2. Double-click the Security Center.
   
   
3. Ensure that the Firewall security essential is marked ON.
   
   Note: If the Firewall security essential is marked on, your Windows Firewall is on and you do not need to continue with these steps.
   
   If the Firewall security essential is not marked on, click the "Recommendations" button.
   
   
4. Under "Recommendations," click Enable Now. A window appears telling you that the Windows Firewall was successfully turned on.
   
   
5. Click Close, and then click OK.
   
   
6. Close the Security Center.

Windows 2000 or Windows XP Service Pack 1 or earlier
Complete the following steps to re-enable the SharedAccess service:

1. Click Start > Run.
2. Type services.msc
   
   Then click OK.
   
   
3. Do one of the following:
   
   • Windows 2000: Under the Name column, locate the "Internet Connection Sharing (ICS)" service and double-click it.
   • Windows XP: Under the Named column, locate the "Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS)" service and double-click it.
     
     
4. Under "Startup Type:", select "Automatic" from the drop-down menu.
   
   
5. Under "Service Status:", click the Start button.
   
   
6. Once the service has completed starting, click OK.
   
   
7. Close the Services window.