VBS.A24

SUMMARY

VBS.A24 is a worm that does little but replicate. It attempts to copy itself across the 24.*.*.* subnet. Any shared drives found on this subnet are subject to infection.

The worm also attempts to remove a VBS.Network infection from the system.

Protection

• Virus Definitions (Intelligent Updater) September 5, 2000

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 50 - 999
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Deletes Files: Network.VBS

Distribution

• Distribution Level: Low
• Shared Drives: Copies itself to shared drives found on the 24.*.*.* subnet.

TECHNICAL DETAILS

VBS.A24 first checks for the existence of the Network.VBS file. If this file is located at C: or C:WindowsStart MenuProgramsStartup, it is deleted. Norton AntiVirus detects the Network.VBS file as VBS.Network.

To copy itself, the worm selects a random IP address found on the 24.*.*.* subnet (e.g., 24.150.1.19) and searches for shared drives. If it finds a shared drive, the drive is mapped locally on the currently infected computer.

The worm then copies itself to the shared drive (c:windowsstartm~1programsstartup) as the file A24.VBS.

Local mappings created by the worm are removed after the worm has executed.

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 remove the worm from the computer, delete all files Norton AntiVirus detects as VBS.A24. These files are located in the WindowsStart MenuProgramsStartup directory.

It is also recommended that you disable sharing on the computer if it is not necessary.