O97M.Tristate | 
|
O97M.Tristate is a Microsoft Office 97 macro virus that has been found in-the-wild. The Symantec AntiVirus Research Center has recently received reports of O97M.Tristate infection through the Scan & Deliver system. The differences among the A, B, and C variants are minor changes to the comments in the macro code.
|
Also Known As: | O97M.Tristate.A, O97M.Tristate.B, O97M.Tristate.C, Macro.Office.Triplicate.C, O97M.Triplicate.C |
|
| |
|
Type: | Worm |
|
Infection Length: | One VBA5 module (and one AutoShape in Microsoft PowerPoint) |
|
| |
|
| |
|
| |
|
| |
|
| |
|
| |
|
| |
|
| |
O97M.Tristate infects Microsoft Word 97 documents, Microsoft Excel 97 spreadsheets, and Microsoft PowerPoint slides. The infection routine in each Microsoft Office application is triggered differently, as described in detail in the following paragraphs.
From an infected Word 97 document
The virus does not add a new Visual Basic Application (VBA) module but inserts its viral code into the default VBA module called ThisDocument. The following viral routine is activated when an infected Word document is closed:
- Crossing to Excel:
If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel macro virus protection (found under Tools Options General). Then it creates a viral workbook called BOOK1 in the Excel startup directory.
- Crossing to PowerPoint:
If there is no Triplicate module in the Blank Presentation.POT PowerPoint template (usually in the TEMPLATES directory), the virus turns off PowerPoint macro virus protection (found under Tools Options General). Then it adds a viral module called Triplicate to Blank Presentation.POT and a basic AutoShape object that covers the entire slide. The viral module is linked to the AutoShape object.
- Re-infecting the Word document being closed, if necessary:
If the ThisDocument module of the document being closed does not match what the virus expects, the virus replaces the content of the ThisDocument module with its viral code.
From an infected Excel 97 spreadsheet:
The virus does not add a new Visual Basic Application (VBA) module but inserts its viral code into the default VBA module called ThisWorkbook. The following viral routine is activated when the infected workbook is deactivated (as in editing another workbook or opening a new one):
- Crossing to Word:
If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel and PowerPoint macro virus protection (found under Tools Options General). Then the virus replaces the content of the ThisDocument module of the Word Normal Template (usually called NORMAL.DOT) with its viral code.
- Crossing to PowerPoint:
If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), and there is no Triplicate module in the Blank Presentation.POT PowerPoint template (usually in the TEMPLATES directory), the virus adds a viral module called Triplicate to Blank Presentation.POT and a basic AutoShape object that covers the entire slide. The viral module is linked to the AutoShape object.
- Re-infecting the Excel spreadsheet being closed, if necessary:
If the ThisWorkbook module of the active spreadsheet does not match what the virus expects, the virus inserts its viral code into the ThisWorkbook module.
From an infected PowerPoint 97 presentation:
In a PowerPoint slide, the virus adds a new Visual Basic Application (VBA) module called Triplicate. The user then has a one in seven chance that the following viral routine will be activated when an infected slide is clicked in a slide show view:
- Crossing to Word:
If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel and PowerPoint macro virus protection (found under Tools > Options > General). Then the virus replaces the content of the ThisDocument module of the Word Normal Template (usually called NORMAL.DOT) with its viral code.
- Crossing to Excel:
If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), the virus turns off Excel macro virus protection (found under Tools > Options > General). Then it creates a viral workbook called BOOK1 in the Excel startup directory.
- Re-infecting the PowerPoint template, if necessary:
If there is no file called BOOK1 in the Excel startup directory (usually called XLSTART), and there is no Triplicate module in the Blank Presentation.POT PowerPoint template (usually in the TEMPLATES directory), the virus adds a viral module called Triplicate to Blank Presentation.POT and a basic AutoShape object that covers the entire slide. The viral module is linked to the AutoShape object.
In PowerPoint, the virus does not directly infect a PowerPoint slide. It infects the Blank Presentation.POT template. Once the template is infected, every new PowerPoint slide that is based on this Blank Presentation template contains the viral module and AutoShape.
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.
Norton AntiVirus users can protect themselves from this virus by downloading the current virus definitions.
Infected Word document repair notes:
In infected Word documents and templates, the virus has replaced any previously written VBA code in the ThisDocument module. Although Norton AntiVirus removes the viral code from the ThisDocument module, it is not possible to restore the overwritten VBA code.
PowerPoint Blank Presentation template file:
Scan and repair the Blank Presentation.POT module. This file is usually in the TEMPLATES directory of Microsoft Office. You might need to turn on ALL-FILE scanning in Norton AntiVirus Option.
Write-up by: Douglas Knowles
|
