cyber flash has discovered two vulnerabilities in Internet Explorer, which can be exploited by malicious people to bypass a security feature in Microsoft Windows XP SP2 and trick users into downloading malicious files.

1) Microsoft Windows XP SP2 has a security feature, which warns users when opening downloaded files of certain types. The problem is that if the downloaded file was sent with a specially crafted "Content-Location" HTTP header or referenced using a specially crafted URL, then in some situations, no security warning will be displayed when the file is opened.

2) An error when saving some documents using the Javascript function "execCommand()" can be exploited to spoof the file extension in the "Save HTML Document" dialog.

Successful exploitation requires that the option "Hide extension for known file types" is enabled (default setting).

A combination of vulnerabilities 1 and 2 can be exploited by a malicious web site to trick a user into downloading a malicious executable file masqueraded as a HTML document.

The vulnerabilities have been confirmed on a fully patched system with Internet Explorer 6.0 and Microsoft Windows XP SP2.

Solution
Disable Active Scripting support and the "Hide extension for known file types" option.

Provided and/or discovered by
cyber flash

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