The Microsoft Outlook View Control is an ActiveX control that allows Outlook mail folders to be viewed via web pages. The control should only allow passive operations such as viewing mail or calendar data. In reality, though, it exposes a function that could allow the web page to manipulate Outlook data. This could enable an attacker to delete mail, change calendar information, or take virtually any other action through Outlook including running arbitrary code on the user's machine. Hostile web sites would pose the greatest threat with respect to this vulnerability. If a user could be enticed into visiting a web page controlled by an attacker, script or HTML on the page could invoke the control when the page was opened. The script or HTML could then use the control to take whatever action the attacker desired on the user's Outlook data.

It also would be possible for the attacker to send an HTML e-mail to a user, with the intent of invoking the control when the recipient opened the mail. However, the Outlook E-mail Security Update, that automatically installs as part of Outlook 2002 would thwart such an attack. The Update causes HTML e-mails to be opened in the Restricted Sites Zone, where ActiveX controls are disabled by default. Microsoft is preparing a patch that will eliminate the vulnerability. However, while this patch is under development, we recommend that customers disable ActiveX controls in the Internet Zone to protect against the web-based scenario discussed above. (The FAQ provides information on how administrators can use Group Policy to make this configuration change network-wide). To protect against the mail-borne scenario, we strongly recommend that Outlook 98 and 2000 users install the Outlook E-mail Security Update if they haven’t already done so. When the patch is complete, Microsoft will re-release this bulletin and provide details on where to obtain the patch and how to use it.