Microsoft has warned two vulnerabilities exist in the HTML Help facility in Windows.
The Help facility includes an ActiveX control that provides much of its functionality. One of the functions exposed via the control contains an unchecked buffer, which could be exploited by a web page hosted on an attacker's site or sent to a user as an HTML mail. An attacker who successfully exploited the vulnerability would be able to run code in the security context of the user, thereby gaining the same privileges as the user on the system.
A second vulnerability exists because of flaws associated with the handling of compiled HTML Help (.chm) files that contain shortcuts. Because shortcuts allow HTML Help files to take any desired action on the system, only trusted HTML Help files should be allowed to use them. Two flaws allow this restriction to be bypassed.
Both flaws affect Windows 98, NT, 2000 and XP.
More information is available on the Microsoft Web site.