Software Engineering Institute

Microsoft Internet Explorer features the ability to process scripting code contained in HTML documents. This feature is known as Active scripting, and one of the supported languages is called JScript. JScript is similar to Netscape's JavaScript, and both languages played some part in the development of ECMAScript, which is defined in ECMA-262.

In JScript, the open method is used to access a document or to open a browser window, and the close method is typically used to close the document or window. The open method takes an argument that specifies either the MIME type (text/html only) of the document or a URL to render in a new browser window.

For security reasons, a script loaded from one site should not be able to access resources on another site, including the local client. In JavaScript, the Same Origin Policy protects clients by ensuring that "when loading a document from one origin, a script loaded from a different origin cannot get or set specific properties of specific browser and HTML objects in a window or frame."

A message posted to the bugtraq mailing list reports that when processing a script containing document.open() without a corresponding document.close(), Internet Explorer allows the script to access local files and other sites without warning, even if the script and the target objects are in different security zones. A script from a potentially malicious site executing in a browser window in the Internet zone is able to access local files via the Document Object Model (DOM) interface. This vulnerability allows an attacker to read cookies and other files of MIME type text/html on the client's file system and also allows an attacker to spoof Internet sites by displaying believable window titles. An attacker who is able to obtain cookies may be able to impersonate a legitimate user and obtain sensitive data such as passwords or credit card information. An attacker could send specially crafted HTML email messages to victims or otherwise convince them to visit a malicious website. Note that in order for this vulnerability to be exploited, Active scripting must be enabled in the security zone in which the email message or web page is rendered.

It has been reported that this vulnerability can also be exploited using document.close().

By convincing a user to view a malicious web page or HTML email message, a remote attacker can read cookies and certain types of files on the target host and spoof Internet sites.

Apply Patch
Apply Q316059 or a more recent cumulative patch for Internet Explorer. See Microsoft Security Bulletin MS02-005 for more information.

Disable Active scripting

To prevent the effects of this vulnerability, disable Active scripting. Instructions for disabling Active scripting can be found in the CERT/CC Malicious Web Scripts FAQ. At a minimum, disable Active scripting in the Internet zone and the zone used by Outlook, Outlook Express, or any other email client that uses Internet Explorer to render HTML.