VBS.Sorry.D

SUMMARY

VBS.Sorry.D is a variant of VBS.Sorry.A. It is a Visual Basic Script worm that copies itself to several folders on a computer hard drive and on network drives. The worm also drops an mIRC configuration file that searches for computers infected with the SubSeven Trojan. It then copies itself and executes on computers that it finds are infected with the SubSeven Trojan.

This worm was previously named VBS.Fonts.C.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (Intelligent Updater) January 8, 2001

Threat Assessment

Wild

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

Damage

• Damage Level: Low
• Deletes Files: Deletes uncommon files and folders.
• Releases Confidential Info: Posts the IP addresses of newly infected computers to various newsgroups.

Distribution

• Distribution Level: Medium
• Shared Drives: Copies itself as sndload.vbs, ttfloader.vbs, or random file names.
• Target of Infection: Also infects computers that are already infected with the SubSeven backdoor Trojan.

TECHNICAL DETAILS

VBS.Sorry.D is a Visual Basic Script worm. This worm is identical in functionality to VBS.Sorry.A except for the activity described in steps 5 and 9.

This worm does the following when it is executed:

1. It tries to determine if a computer is already infected. If the worm finds multiple copies of itself on the computer, it deletes the extra copies. The worm then deletes the following files, which are common names of other well-known viruses:
   • Network.vbs
   • Msfg.vbs
   • Winsock.vbs
   • A24.vbs
   • Mscfg.exe
   • Ashield.pif
   • Netstat.pif
     
2. The virus copies itself to C:WindowsFontsTtfloader.vbs. If the worm is not running from the Startup folder, or if it is not named Ttfloader.vbs, it deletes itself, displays the following message, and exits:
   
   
   
3. The worm then attempts to execute Ttfloader.vbs from the WindowsFonts folder and makes the following changes to the Windows registry:
   
   • To the key:
     
     HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
     
     it adds the value:
     
     tfload = wscript.exe windowsfonts tfloader.vbs
     
   • To the key:
     
     HKEY_CURRENT_USERSoftwareMicrosoftWindows Script HostSettings
     
     it adds the value:
     
     Timeout = 0
     
   • In the key:
     
     HKEY_LOCAL_MACHINESoftwareMicrosoftInternet ExplorerMain
     
     it adds or changes the value to:
     
     Start Page = http://www.zonelabs.com/
     
     (This enables the virus to start on reboot, never time out when making network connections, and changes the Internet Explorer start page.)
     
4. The worm begins to find locations to which it can copy itself. The worm enumerates all drives (including mapped drives).
   • If the drive is a hard drive or a RAM drive, the worm checks for mIRC folders, where it creates a viral Script.ini file and then copies itself to the WindowsFonts folder as Sndload.vbs.
   • If the worm finds folders where the name matches anything in the following list, it copies itself to that folder using a randomly selected file name. (The random file name is generated from the Recent Documents list.)
     • pub
     • ftproot
     • wwwroot
     • my
     • download
     • upload
     • share
     • game
     • warez
   • Spaces are appended to the base file name and the extension .vbs is added. For example, if Readme.txt is in the Recent Documents list, the worm will use the file name: Readme.txt .vbs.
   • If the worm finds folders that match the following names, it will delete those folders:
     • chode
     • foreskin
     • d_ckhair
   • If the drive is a removable drive (including floppy drives) or a network drive, the worm copies itself to the drive using the same random file name algorithm. The worm also searches for folders matching Drive:*win*StartUp and copies itself as Sndload.vbs. This is generally the Windows StartUp folder. The worm copies itself to folders matching the strings in the following list using a random file name as it did earlier :
     • share
     • download
     • downloads
5. The worm begins searching for open shares on specific subnets. The worm creates a temporary file with randomly generated IP addresses targeting some subnets more than others. The worm will randomly choose a subnet from one of the following groups:
   • 24.*.*.*
   • 172.128.*.*
   • 38.0-254.*.*
   • 205.163.*.*
   • 4.0-254.*.*
   • 151.196-206.*.*
   • 63.194-207.*.*
   • 216.76-79.*.*
   • 3-243.*.*
6. The worm pings each IP address and determines if there is a reply.
7. The worm obtains all the open shares on the computer and maps the network share. It then searches for folders matching Drive:*win*Startup and copies itself as Sndload.vbs. If the worm finds any of the folders in the following list, it copies itself as a random file name using the Recent documents list and appending the .vbs extension.
   • share
   • download
   • downloads
8. The worm removes the network drive.
9. Each time that the worm copies itself to another computer, it adds a line that contains the IP address of the other computer (that it infected) to the text file WindowsSystemTtfload.dll. This information is also posted to various newsgroups using Microsoft Outlook.

If the computer is infected with the additional mIRC component, the worm will search for computers infected with the SubSeven Trojan, where it will upload and execute itself.

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

To repair damage done by the worm, you need to complete the following tasks:

• Delete all files that Norton AntiVirus (NAV) detects as infected by VBS.Sorry.C.
• Restore the Internet Explorer Start Page if desired.
• Delete or the registry entries made by the worm.

Please refer to the appropriate sections for instructions on complete each task.

To delete the infected files:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start NAV and run a full system scan. Unless you are using NAV 2001, make sure that NAV is set to scan all files.
3. Delete any files that are detected as infected with VBS.Sorry.C.
4. Delete the file ttfload.dll from the WindowsSystem directory.

To restore the Internet Explorer Start Page:

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

To remove the registry entries made by the worm:

CAUTION: We strongly recommend that you back up the system registry before making any changes to it. Incorrect changes to the registry may result in permanent data loss or corrupted files. Be sure to modify the specified keys only. See the document How to back up the Windows registry before proceeding.

1. Click Start, and then click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Browse to and select the following subkey:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, locate and delete the following value:
   
   tfload = wscript.exe windowsfonts tfloader.vbs
   
5. Browse to and select the following subkey:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindows Script HostSettings
   
6. In the right pane, locate and delete the following value:
   
   Timeout = 0
   
7. Close the Registry Editor.