Winword Macro Viruses

Winword Macro Viruses Privacy and Legal Notice INFORMATION BULLETIN G-10a: Winword Macro Viruses February 8, 1996 18:00 GMT

PROBLEM:       Word macro viruses are no longer an isolated threat, but they are
                a significant hazard to the information on a computer.
PLATFORM:      Any platform that can run Microsoft Word 6.0 or later: 
                Windows 3.1, WFW 3.11, Win 95, Windows NT, and Macintosh.
DAMAGE:        Files can be deleted and may not be recoverable.
SOLUTION:      Scan all new Word documents before opening them in the same way 
                that you now scan all executable files before running them. 
                Install version 2 of the Microsoft macro virus detection tool.
VULNERABILITY  The vulnerability of systems to this type of virus is high, 
ASSESSMENT:    because most users are not in the habit of scanning documents. 
                 Documents are much more mobile than executable files in an 
                 organization, passing from machine to machine as different 
                 people write or edit them.

CRITICAL Information Concerning Winword Macro Viruses

CIAC has obtained information about six macro viruses currently in the wild, five of which infect Microsoft Word 6.0 documents, and one that infects an Excel worksheet. Two of these viruses are damaging. This bulletin describes these viruses:

: Concept (Prank) Working demo of a macro virus.
: DMV (Word) Working demo of a macro virus.
: DMV (Excel) Working demo of a macro virus.
: Nuclear Attempts damage but fails.
: Colors Changes screen colors.
: FormatC Deletes files on the hard drive.
: Hot Deletes Word documents when they are opened.

WARNING: The new macro viruses are not detected by the original protection macro available from Microsoft which only detects Concept (scan831.dot, see CIAC Notes 95-12). A new protection program is available from Microsoft and most anti-virus scanner developers are adding macro virus detection to their products. The new Microsoft scanner is available from Microsoft at:

http://www.microsoft.com/msoffice/freestuf/mvtool/mvtool10.exe

with a description available at:

http://www.microsoft.com/msoffice/freestuf/mvtool/mvtool2.htm

The files are also available from the CIAC archive.

WARNING: The new macro virus detector from Microsoft only scans files if they are opened with the File-Open command in Word and not if they are opened by double-clicking the document or by selecting the document from the recent documents list at the bottom of the File menu. You must use the File-Open command to activate the protection.

What Are Macro Viruses?

A macro virus is a piece of self-replicating code written in an application's macro language. Many applications have macro capabilities such as the automatic playback of keystrokes available in early versions of Lotus 1-2-3. The distinguishing factor which makes it possible to create a virus with a macro is the existence of auto-execute macros in the language. An auto-execute macro is one which is executed in response to some event and not in response to an explicit user command. Common auto-execute events are opening a file, closing a file, and starting an application. Once a macro is running, it can copy itself to other documents, delete files, and create general havoc in a person's system. These things occur without the user explicitly running the macro.

In Microsoft Word there are three types of hazardous, auto-executing macros: auto-execute macros, auto-macros, and macros with command names. There is one auto-execute macro in Word named AutoExec. If a macro named AutoExec is in the "normal.dot" template or in a global template stored in Word's startup directory, it is executed whenever Word is started. The only way to disable the execution of AutoExec is to insert the flag /m in the command line used to start Word.

The second type of dangerous macros are auto-macros.

Name Runs when you ------------------------------------ AutoNew create a new document. AutoOpen open a document. AutoClose close a document. AutoExit quit Word.

The auto-macros can be disabled by executing the Word.Basic command "DisableAutoMacros" in a macro. Note that the example in Word's online help of executing this command in the command line when starting Word does not work. The command must be executed in a macro. Auto-macros are also disabled by holding down the shift key while opening a document.

The third type of dangerous macros are those named for an existing Word command. If a macro in the global macro file or in an attached, active template has the name of an existing Word command, the macro command replaces the Word command. For example, if you create a macro named FileSave in the "normal.dot" template, that macro is executed whenever you choose the Save command on the File menu. There is no way to disable this feature.

Macro viruses spread by having one or more auto-execute macros in a document. By opening or closing the document or using a replaced command, you activate the virus macro. As soon as the macro is activated, it copies itself and any other macros it needs to the global macro file "normal.dot". After they are stored in normal.dot they are available in all opened documents.

At this point, the macro viruses try to spread themselves to other documents, usually by including an AutoClose macro that attaches the virus macros to the document and saves it. The macro viruses that cause damage contain a trigger that starts the damage routines and those routines do the actual damage. The trigger is some event that the virus writer has programmed his virus to watch for such as a date or the number of days since the infection occurred.

An important point to make here is that Word documents (.DOC files) can not contain macros, only Word templates (.DOT files) can contain macros. However, it is a relatively simple task to mask a template as a document by changing the file name extension from .DOT to .DOC.

DMV (Word) Macro Virus

The DMV (Demonstration Macro Virus) virus was originally described in the paper "Document Macro Viruses" by Joel McNamara who conveniently infected the document containing the paper with the virus so the reader could experience it first hand. The virus itself is simply an example of how such a virus could be implemented and does not attempt to hide itself at all. The virus is not harmful and is relatively simple to remove using the Tools Macro command in Microsoft Word (See below). The virus installs a single macro named AutoClose onto the "normal.dot" global macro file. The AutoClose macro infects all new documents when they are closed. The macro does no damage other than to spread itself. When the macro runs, it displays numerous dialog boxes telling you what it is doing, making it obvious if you are infected.

DMV (Excel) Macro Virus

The Excel version of the DMV macro virus works the same as the Word version but uses the Visual Basic for Applications language built into Excel. The Excel document contains a macro sheet which implements an AutoClose macro. When you close the file, the macro is activated and copies itself to Excel's global macro file. When other worksheets are closed, the macro attaches itself to them as well.

Concept (Prank) Macro Virus

The Concept macro (alias Prank) is similar to the DMV macro virus in that it is a demonstration that a macro virus can be created. A document infected with the Concept virus contains the macros:

          AAAZAO     AutoOpen
          AAAZFS     Payload

When an infected file is opened the AutoOpen macro is run and copies the virus files to the global macro file. During the copying process, it changes the name of AAAZFS to FileSaveAs. Whenever a document is saved, the FileSaveAs command copies the virus macros into it and saves it. The AAAZAO macro becomes the AutoOpen macro on the saved document file. The Payload macro does nothing. The first time the macro runs a dialog box appears with the single digit "1" contained in it.

Nuclear Macro Virus

A document infected with the Nuclear macro virus contains nine macros:

          AutoExec        AutoOpen        DropSuriv
          FileExit        FilePrint       FilePrintDefault
          FileSaveAs      InsertPayload   Payload

All of these are copied to the global macro file when an infected document is opened. When any document is saved, the virus copies all the macros onto it and saves it. Printing a document during the last 5 seconds of any minute causes the following text to appear at the top of the printed page:

"And finally I would like to say:"

"STOP ALL FRENCH NUCLEAR TESTING IN THE PACIFIC!"

After April 5th, it attempts to delete your system files but fails because of a bug in the virus. The virus also attempts to infect a system with the Suriv binary virus, but fails again because of a bug.

Colors Macro Virus

A document infected with the Colors virus contains the following eight macros:

          AutoClose        AutoExec        AutoOpen
          FileExit         FileNew         FileSave
          FileSaveAs       ToolsMacro

The virus changes many of the menu items to make it difficult to delete. For example, it effectively removes the Tools Macros command so you can't list or delete the macros in a program with that command.

After being accessed 300 times, Colors activates and randomly changes the system colors in the win.ini file making the screen look strange.

FormatC Macro Virus

The FormatC macro virus consists of a single macro named AutoOpen. Opening an infected document causes this macro to run and the macro copies itself to the global macro file. If the viruses payload is activated, it attempts to format the C: drive.

WARNING: The format command in most modern versions of DOS can be reversed. If this virus strikes, get some knowledgeable help before doing anything to your system. Don't do anything that might write something on the hard drive until you get knowledgeable help. You may need only boot from a floppy and run unformat to recover the whole drive. What you do depends on what utility programs (Norton Utilities, PCTools, and so forth) you have installed on your system.

Wordmacro/Hot

A new Word macro virus just appeared in the wild named Wordmacro/Hot and it is destructive. The Wordmacro/Hot virus attaches itself like the others, adding macros to documents and to the "normal.dot" global macro file. New documents are infected when they are saved. After about 14 days, the virus deletes the contents of any document as you open it and does a save which effectively wipes out the document. It is unlikely that you will be able to recover the contents of a file deleted in this way unless you have Make Backup turned on. Don't start opening the backup copies before cleaning the virus, because it will clear the contents of every document you open while it is active.

An infected document contains the following macros:

   AutoOpen     DrawBringInFrOut     InsertPBreak     ToolsRepaginat

When the virus infects the Word program, these macros are copied to "normal.dot" and renamed in the same order to:

   StartOfDoc   AutoOpen             InsertPageBreak  FileSave

The virus adds the item: "OLHot=nnnnn" to the winword.ini file where nnnnn is a date 14 days in the future. The virus uses this date to determine when it is going to trigger. The virus also checks for the existence of the file: "c:\dos\ega5.cpi" and does not infect a machine if the file exists. This was apparently a feature to protect the virus writer.

Detecting A Macro Virus

Document files must now be treated in the same manner as executables in terms of virus protection. If you don't know where a Word document has been, scan it before opening it with Word. Most anti-virus scanners have been modified to detect macro viruses in Word documents, so use those scanners to check any new documents that have been copied onto your machine. For example, version 2.21 of the shareware version of F-Prot detects all but the FormatC and Hot viruses.

Microsoft has released a new version of its macro virus protection program (see below) that checks all Word documents as you open them with the File-Open command and tells you if they contain a macro or not. It can only detect the Concept virus by name, but any document with a macro attached should be considered suspect.

You can use the Organizer dialog box (see below) to check for strange macros attached to your documents. The Organizer can open a document in the background (without running any attached macros) and let you see what macros are attached to it. You can also use it to delete macros from a document.

You can watch for virus activity when opening or saving a document, but it is generally preferable to detect a virus before it gets installed. If you have already opened a document that suspect has a virus, use the Tools Macro command to see a list of the macros attached to Word. If you can't open the Macro dialog box, try the Organizer dialog box instead.

Protecting A System From Macro Viruses

A feature of Microsoft's products is that automatic execution of auto- macros and auto-execute macros is enabled by default. In fact, it is difficult to turn off. This is a problem in protecting against macro viruses.

Currently, the best protection is to install Microsoft's macro virus protection template. The template is available directly from Microsoft's web site or from the CIAC archive. A description of the scanner is available at:

http://www.microsoft.com/msoffice/freestuf/msword/download/mvtool/mvtool2.htm

and the scanner itself is available at:

http://www.microsoft.com/msoffice/freestuf/msword/download/mvtool/mvtool10.exe

If you don't find these files at microsoft.com, it could be that the scanner has been revised again. In that case, connect to:

http://www.microsoft.com

and use the search command to search for "macro virus".

WARNING: The new macro virus detector from Microsoft only scans files if they are opened with the File-Open command in Word and not if they are opened by double-clicking the document or by selecting the document from the rec ent documents list at the bottom of the File menu. You must use the File-Open comman d to activate the protection.

To install the macro virus protection, simply open the template file with Word and follow the instructions. The macros automatically install themselves in your global macro file (just like the virus). A protected version of Word should have the following four macros attached to the "normal.dot" file:

        AutoExit     FileOpen     InstVer    ShellOpen

FileOpen calls ShellOpen whenever a document is opened. ShellOpen checks each newly opened document to see if it has any macros attached. If there are macros in the document that is being opened, ShellOpen displays a dialog box giving you the choice to open the document anyway, remove the macros and open it, or cancel the open command.

If, for some reason, you can't use Microsoft's protection macro, you can disable auto-macros. You have three options:

1. Disable the auto-macros.
2. Disable the auto-macros and the auto-execute macro.
3. Hold down Shift whenever you open a file to disable the AutoOpen macro.

To disable auto-macros, create the following macro named AutoExec in the global macro file (normal.dot).

MAIN
   DisableAutoMacros 1
   MsgBox "Auto-macros are disabled."
End Sub

All auto-macros are disabled but a virus could still infect a system if it is activated by a command that replaces a normal command.

To disable auto-macros and the auto-execute macro, create the following macro in the global macro file (normal.dot) and name it "DisableMyAutoMacros".

MAIN
   DisableAutoMacros 1
   MsgBox "Auto-macros are disabled."
End Sub

In the Program Manager or the Explorer in Windows 95, select the Word icon and choose the Properties command on the File menu. Add the following switch to the command line for Word.

/mDisableMyAutoMacros

This command disables the AutoExec macro and runs the DisableMyAutoMacros procedure when Word starts up. Again, this does not disable macros with command names from replacing the commands. This also only works if you start Word by double clicking on the Word icon. If you start Word by double clicking on a document, it will not see the switch and will not run the DisableMyAutoMacros procedure.

When you hold down the Shift key while opening or double clicking a document, the AutoOpen macro is prevented from running. Other auto-macros may still run so you must check for a virus before doing anything else.

WARNING: The three methods of disabling auto-macros and the auto-execute macro do not fully protect you from a virus. While they prevent the auto-execute and auto-macro commands from running, they do not prevent any macros named the same as commands from replacing those commands. Any virus that uses replaced commands to initiate an infection will not be stopped. Only an external scanner or the Microsoft template will detect a document containing macros before it is opened.

Removing Macro Viruses

If you have an anti-virus scanner which detects and removes a macro virus, use it instead of trying to do it by hand. The scanner will generally do the job and is much easier than removing the virus by hand.

If you have Microsoft's virus macro protection installed, it will give you the option to remove any attached macros when you open the document. If you save the document with the same name, it will overwrite the infected document.

If you don't have a scanner or the protection macro, you can use the Organizer to find and remove macro viruses without infecting your system. The first step is to start Word and open the Organizer dialog box. There are two ways to open the Organizer: 1. use the Tools Macro command and press the Organizer button; 2. use the File Templates command and press the Organizer button. In the Organizer dialog box click the macros tab, click the Open File button, select the infected document and click OK. Back in the Organizer dialog box, select all the macros listed in the file and click the Delete button to remove them. Click the Close File button to close and save the file. The file can now be opened normally.

If you have just infected yourself by opening an infected document, don't close the document or quit Word. If you close the infected file or quit Word, you run the risk of running another of the auto-execute macros. See if you can get to the Organizer dialog box. Once in the Organizer you can delete the virus macros from the infected document and from the "normal.dot" file. Save those files, quit Word and restart it. You can then use the Organizer to check other documents for a virus infection.

If you can't get to the Organizer, quit Word without saving anything, find the "normal.dot" file and delete it. When you restart Word, it will create a new, empty "normal.dot" file. Note that you will also lose any custom styles which were stored in the "normal.dot" file and will have to redefine them.

On The Macintosh

These macro viruses will run under Word 6 on the Macintosh, but most of the file access capability used by the viruses to damage a system will not work well. This is because file naming conventions on the Macintosh are different from those on other systems. Since the damaging parts of the viruses are written with a DOS-based file system in mind, it is unlikely that they will work.

Macro Viruses and E-Mail Messages

Many rumors have been circulated around the network about there being an e-mail message that destroys your system when you read it (Good Times). This can not happen with the current batch of mail readers. While an infected document could be attached to an e-mail message and would be downloaded to your disk when you read the attached message, it will not automatically be executed. As long as it has not been executed or read, it can not infect your system with a virus. At this point, you should scan it to make sure it is not infected.

Conclusions

Macro viruses are here to stay and we must deal with them in the same manner that we have had to deal with other viruses. If you don't know where a file has been, don't use it in your computer until you scan it. That is, if it is an executable, don't run it; if it is a document, don't open it. It does not matter how you obtained the file, whether it is a download from a BBS or web site, an attachment to an e-mail message, or a shrink-wrapped package from a commercial developer, scan them all. Even blank, preformatted disks are occasionally showing up with viruses.

The second thing to do is to install the Microsoft macro virus protection template to warn you if a document contains macros before you open it.

Keep in mind that while Microsoft products are being targeted by these viruses, they are not the only products which have a macro capability which could be exploited. Hopefully, in the next release of software programs which include extensive macro capabilities, there will be an easy way to disable macro execution and warn the user if documents contain macros. This change will make the problem of macro viruses go away very quickly.

CIAC wishes to acknowledge the help of Michael Messuri and Charles Renert of Symantec Corp. and Chuck Noble of Digital Equipment Corp. for valuable assistance in the preparation of this bulletin.

CIAC services are available to DOE, DOE Contractors, and the NIH. CIAC can be contacted at:

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