W32.Sobig.E@mm

SUMMARY

Due to a decreased rate of submissions, and the hard coded deactivation date, Symantec Security Response has downgraded this threat to a Category 2 from a Category 3 as of July 16, 2003.

W32.Sobig.E@mm is a mass-mailing, network-aware worm that sends itself to all the email addresses that it finds in the files with the following extensions:

• .wab
• .dbx
• .htm
• .html
• .eml
• .txt

The email falsely purports that Yahoo sent it (support@yahoo.com).

Email Routine Details
The email message has the following characteristics:

From: support@yahoo.com (NOTE: W32.Sobig.E@mm spoofs this field. It could be any address.)

Subject: The subject line will be one of the following:

• Re: Application
• Re: Movie
• Re: Movies
• Re: Submitted
• Re: ScRe:ensaver
• Re: Documents
• Re: Re: Application ref 003644
• Re: Re: Document
• Your application
• Application.pif
• Applications.pif
• movie.pif
• Screensaver.scr
• submited.pif
• new document.pif
• Re: document.pif
• 004448554.pif
• Referer.pif
  

Attachment: The attachment name will be one of the following:

• Your_details.zip (contains Details.pif)
• Application.zip (contains Application.pif)
• Document.zip (contains Document.pif)
• Screensaver.zip (contains Sky.world.scr)
• Movie.zip (contains Movie.pif)

NOTE: The worm de-activates on July 14, 2003, and therefore, the last day on which the worm will spread is July 13, 2003. While the worm no longer attempts to spread, it will still attempt to perform an update during the trigger period referenced below.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 25, 2003
• Virus Definitions (Intelligent Updater) June 25, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: More than 1000
• Number of Sites: More than 10
• Geographical Distribution: Medium
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Large Scale E-mailing: Sends email to addresses collected from files with the following extensions: .wab, .dbx, .htm, .html, .eml, .txt.
• Releases Confidential Info: May steal system information including passwords.

Distribution

• Distribution Level: High
• Subject of Email: Varies
• Name of Attachment: Varies with .zip extension.
• Size of Attachment: 82,195 bytes
• Ports: UDP 123, 995, 996, 997, 998, 999, 8998
• Shared Drives: Attempts to copy itself to shared resources.

TECHNICAL DETAILS

When W32.Sobig.E@mm is executed, it performs the following actions:

1. Copies itself as %Windir%winssk32.exe.
   
   NOTE: %Windir% is a variable. The worm locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to that location.
   
   
2. Creates the file, %Windir%msrrf.dat.
   
   
3. Adds the value:
   
   "SSK Service"="%Windir%winssk32.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   so that W32.Sobig.E@mm runs when you start Windows.
   
   
4. If the operating system is Windows NT/2000/XP, then the worm will also add the value:
   
   "SSK Service"="%Windir%winssk32.exe"
   
   to the registry key:
   
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
5. Counts the Network Resources and copies itself across the network to the following folders:
   • WindowsAll UsersStart MenuProgramsStartUp
   • Documents and SettingsAll UsersStart MenuProgramsStartup
     

Sobig.E can download arbitrary files to infected computers and execute them. The author of the worm has used this functionality to steal confidential system information and to set up spam relay servers on infected computers.

This functionality may also be used as a worm self-update feature. Under the correct conditions, Sobig.E attempts to contact one of the list of master servers, which the author of the worm controls. Then, the worm retrieves a URL that it uses to determine where to get the Trojan file, downloads the Trojan file to the local computer, and then executes it.

In Sobig.E, the conditions for this download attempt are the following:

• According to UTC time, the day of the week must be Monday or Friday.
• According to UTC time, the time of the day must be between 7:00 P.M. and 11:59:59 P.M.

The following represents the list of IP addresses correlating to the master servers:

• 129.244.36.194
• 218.146.139.246
• 66.169.84.77
• 67.164.250.26
• 67.73.60.121

Sobig.E obtains the UTC time through the NTP protocol, by contacting one of several possible servers on port 123/udp (the NTP port).

The worm starts the download attempt by sending a probe to port 8998/udp of the master server. Then, the server replies with a URL, where the worm can download the file to execute.

Sobig.E also opens the following ports:

• 995/udp
• 996/udp
• 997/udp
• 998/udp
• 999/udp

and it listens for any incoming UDP datagrams on these ports. Incoming datagrams are parsed, and upon receiving a datagram with the proper signature, the master server list of the worm may be updated.


Network administrators should do the following:

• Block inbound traffic on ports 99x/udp.
• Block outbound traffic on port 8998/udp.
• Monitor NTP requests (port 123/udp), as these could be coming from infected computers. (The frequency of such checks for an infected computer should be once per hour.)

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.Sobig.E@mm Removal Tool
Symantec Security Response has created a tool to remove W32.Sobig.E@mm, which is the easiest way to remove this threat.

Manual Removal
As an alternative to using the removal tool, you can manually remove this threat.

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

NOTE: If you are on a network or have a full-time connection to the Internet, disconnect the computer from the network and the Internet. Remove this threat from all the computers on the network before you reconnect to it. Disable or password-protect file sharing before reconnecting the computers to the network or to the Internet. For instructions on how to do this, see your Windows documentation, or the document, "How to configure shared Windows folders for maximum network protection."

IMPORTANT: Do not skip this step. Disconnect from the network before attempting to remove this worm.

1. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the Trojan process.
4. Run a full system scan and delete all the files detected as W32.Sobig.E@mm.
5. Find and delete the files using the Windows Find or Search utility.
6. Delete the values that were added to the registry.
   

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"

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. Restarting the computer in Safe mode or ending the Trojan process

Windows 95/98/Me
Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

Windows NT/2000/XP
To end the Trojan process:
1. Press Ctrl+Alt+Delete once.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to alphabetically sort the processes.
5. Scroll through the list and look for Winssk32.exe.
6. If you find the file, click it, and then click End Process.
7. Exit the Task Manager.

4. 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.Sobig.E@mm, click Delete.

5. Finding and deleting files

Follow the instructions for your operating system:

• Windows 95/98/Me/NT/2000
  1. Click Start, point to Find or Search, and then click Files or Folders.
  2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
  3. In the "Named" or "Search for..." box, type, or copy and paste, the filename:
     
     msrrf.dat
     
     
  4. Click Find Now or Search Now.
  5. Delete the displayed files.
  
  
• Windows XP
  1. Click Start, and then click Search.
  2. Click All files and folders.
  3. In the "All or part of the file name" box, type, or copy and paste, the filename:
     
     msrrf.dat
     
     
  4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
  5. Click "More advanced options."
  6. Check "Search system folders."
  7. Check "Search subfolders."
  8. Click Search.
  9. Delete the displayed files.
  
  

6. Deleting the values from the registry

CAUTION: 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.

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_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the value:
   
   "SSK Service"="%Windir%winssk32.exe"
   
   
5. If the operating system is Windows NT/2000/XP, navigate to the key:
   
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
6. In the right pane, delete the value:
   
   "SSK Service"="%Windir%winssk32.exe"
   
   
7. Exit the Registry Editor.