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. First, the HTML Help facility incorrectly determines the Security Zone in the case where a web page or HTML mail delivers a .chm file to the Temporary Internet Files folder and subsequently opens it. Instead of handling the .chm file in the correct zone – the one associated with the web page or HTML mail that delivered it – the HTML Help facility incorrectly handles it in the Local Computer Zone, thereby considering it trusted and allowing it to use shortcuts. This error is compounded by the fact that the HTML Help facility doesn’t consider what folder the content resides in. Were it to do so, it could recover from the first flaw, as content within the Temporary Internet Folder is clearly not trusted, regardless of the Security Zone it renders in.

The attack scenario for this vulnerability would be complex, and involves using an HTML mail to deliver a .chm file that contains a shortcut, then making use of the flaws to open it and allow the shortcut to execute. The shortcut would be able to perform any action the user had privileges to perform on the system.

Patch availability

Download locations for this patch
The patches for all Windows systems are available via Windows Update or can be manually applied via the following patches:

• Windows 98 and Windows 98 SE:
  http://www.microsoft.com/windows98/downloads/contents/WUCritical/q323255/default.asp
• Windows Me:
  Only available via Windows Update.
• Windows NT 4.0:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=43308
• Windows NT 4.0, Terminal Server Edition:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=43308
• Windows 2000:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=40213
• Windows XP Home Edition and Professional Edition:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=41834