W97M.Heathen.12288.A

SUMMARY

W97M.Heathen.12288.A is another attempt to combine the macro virus spreading power with Win32 programs. The virus is rather buggy. It does not work under Windows 98 or Windows NT. Even when it works under a Windows 95 system, the modified EXPLORER.EXE becomes unstable. It may also crash MS Word 97 after it infects the system.

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: Similar to the way it tricks Windows to replace EXPLORER.EXE with HEATHEN.VEX, the virus adds a WININIT.INI file that contains: [rename] nul=System.dat nul=User.dat nul=System.da0 nul=User.da0 This instruction makes Windows delete the Registry files when it starts. The payload is triggered six months after the original infection.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Upon opening an infected Word 97 document, the following events occur:
1. AutoOpen routine of the virus creates "HEATHEN.VDO", an OLE storage file, into the WINDOWS directory. This OLE storage file holds the viral macro structure to be added into the targeted Word 97 document.
2. It then proceeds to drop "HEATHEN.VDL", a Win32 program, into the WINDOWS directory. This file contains the routine to infect MS Word 97 documents.
3. The virus modifies EXPLORER.EXE in the WINDOWS directory. The modification adds a loading routine such that HEATHEN.VDL gets loaded every time EXPLORER.EXE is executed.
4. If it fails to modify EXPLORER.EXE (the file is read only, or being used, etc), it will copy EXPLORER.EXE into HEATHEN.VEX. Then, it modifies HEATHEN.VEX. To have EXPLORER.EXE replaced by HEATHEN.VEX, the virus creates a WININIT.INI file that contains:

[rename]

C:WINDOWSExplorer.exe=C:WINDOWSHeathen.vex

This instruction in the WININIT.INI file makes Windows replace EXPLORER.EXE with the HEATHEN.VEX file upon the next startup.

When a modified EXPLORER.EXE runs, the following events occur:
1. HEATHEN.VDL gets loaded. The infection routine runs in the background, scanning all available drive letters.
2. Then, it searches for .DOC and .DOT files.
3. If the .DOC or .DOT file has no macro, it adds the macro stored in HEATHEN.VDO into the target file.

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

NAV detects and repairs infected MS Word 97 documents.

NAV detects the HEATHEN.VDO file as "W97M.Heathen.12288.A". However, NAV will fail to repair because it sees this file as an incomplete (potentially corrupted) MS Word 97 document. NAV stops the repair to prevent further corruption.

NAV detects the HEATHEN.VDL file as "Heathen.12288(DLL)". This file needs to be deleted.

Unfortunately, the modification to EXPLORER.EXE is irreversible. EXPLORER.EXE needs to be restored from a clean copy. A clean copy of EXPLORER.EXE can be found on the Windows Installation CD:
· in WIN95_10.CAB file for Windows 95a
· in WIN95_17.CAB file for Windows 95b
· in WIN98_41.CAB file for Windows 98 (although it does not work in Windows 98)

CAB files may be extracted using a CAB file viewer (downloadable from Microsoft website) or using an archive utility such as WinZip.