The flaw is in an ActiveX control called the Certificate Enrollment Control, used to request new digital certificates over the Web and install them on computers. An internal security investigation revealed that the Certificate Enrollment Control can be used to delete or corrupt digital certificates, instead of installing them, according to Microsoft Security Bulletin MS02-048.
The certificates are used in a number of functions by Windows operating systems, including encrypting e-mail, securing and authenticating Web transactions, or protecting the Windows 2000 and Windows XP Encrypting File Systems. If the certificates are deleted or corrupted, then access to the affected functions may be denied.
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The attack could be carried out by creating a Web page to exploit the flaw. By hosting the page on a Web site, it could be used to attack the computers of visitors to the page. Another possibility would be to send the page in an HTML mail; the vulnerability could then be exploited when the mail was opened.
The flaw affects Windows 98, 98SE, Millennium Edition, NT 4.0, 2000 and XP, Microsoft said. It might also affect earlier versions of the operating system, but these were no longer supported and so had not been tested, it said.
To fix the problem, Microsoft recommends installing a patch that disables the flawed ActiveX control by setting its "kill bit" and replacing it with a new control. This means that any Web site that genuinely uses the affected control will need to be redesigned to use the new version instead.
The patch also fixes a similar flaw in another ActiveX control, the SmartCard Enrollment control, part of Windows 2000 and Windows XP.
The IDG News Service is a Network World affiliate.
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