W97M.Chantal.B

SUMMARY

W97M.Chantal.B is a variant of W97M.Chantal.A. It utilizes DOS Batch scripting (BAT), Visual Basic for Application (VBA) and Visual Basic Scripting (VBS).
It also uses the Year 2000 as its malicious-payload trigger date.

Threat Assessment

Wild

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

Damage

• Damage Level: Low
• Payload Trigger: It uses the Year 2000 as its malicious-payload trigger date.
• Deletes Files: The payload is to delete all files from C: (the root directory of C: drive) and from the current directory (the directory where the infected document resides).

Distribution

• Distribution Level: Low
• Target of Infection: Microsoft Word 97

TECHNICAL DETAILS

When opening an infected document, this virus immediately inserts a VBS file, C:WINDOWSSYSTEMMKV2.VBS, and registers it to run every time Windows starts. This VBS file is used to re-infect Microsoft Word Global Template (usually NORMAL.DOT) every time Windows starts. The VBS program uses a temporary text file C:WINDOWSMKV4.VXD in re-infecting MS Word Global Template.

Then, it inserts a DOS Batch file, C:MKV2.BAT, and adds a line in C:AUTOEXEC.BAT to execute this inserted BAT file. This BAT file is a virus on its own. It is a BATch virus that is designed to append itself to every BAT file in the current directory and its parent directory. However, the BAT script is poorly written that it will only append itself to a BAT file in the root directory.

The infection routine of this virus is very ordinary. In fact, Bloodhound heuristic easily detects this macro virus.

Payload

There are several payloads in this macro virus, and one of them is malicious. The malicious payload gets triggered on Year 2000. The payload is to delete all files from C: (the root directory of C: drive) and from the current directory (the directory where the infected document resides). At the same time, it displays a message box entitled MK Words V2 By MKVG 1999 with a message:

Welcome To Y2K

On the 31st day of every month, it displays a similar message as a balloon message from the Office Assistant:

Y2K is Coming Soon...

It also sets the comment field in the document summary info to:

MK-Words (V2) By MMK 1999

Childishly, this virus changes the Windows Registered Owner to "Mae Koo V-Groups" and the Windows version number to MKV-99.

Hiding its activity

Similar to most macro viruses, this macro virus tries to hide its activity by disabling the following:
· Tools-Macro menu item
· Prompt to save Normal template
· Confirm conversion at Open
· Macro virus protection

With these options disabled, MS Word 97 does not warn or prompt while saving the NORMAL.DOT or while opening a document with macro in it.

In MS Word 2000, this macro virus also sets the security level to zero.

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 files should be deleted:
· C:WINDOWSSYSTEMMKV2.VBS (detected as VBS.Chantal.B)
· C:WINDOWSMKV4.VXD

Please do the following also:

The registry entry that calls MKV2.VBS needs to be removed. To do this, run REGEDIT and search for MKV2.VBS. You may also want to restore the Windows version and the Windows Registered Owner.

C:AUTOEXEC.BAT needs to be edited manually to remove the line @MKV2.BAT that runs the virus file.

The hidden C:MKV2.BAT file must be deleted. Norton AntiVirus detects it as BAT.Chantal.B.

Any BAT-file that Norton AntiVirus detects as BAT.Chantal.B needs to be edited manually to remove the viral code.