IE users warned: Close cookie jar

Thousands of ecommerce sites use cookies to authenticate users or store private information. However, those cookies could be exposed by IE and intercepted by a third-party website, according to internet privacy watchdog group Peacefire.org.

Peacefire demonstrated that by using a specially constructed URL, a site can read IE cookies.

For example, to read an Amazon.com cookie, a site might direct the user's browser to www.peacefire.org%2fsecurity%2fiecookies%2fshowcookie.html%3F.amazon.com.

Peacefire points out that if the "%2f"'s are replaced with "/" characters, and the "%3F" with "?", this URL is actually www.peacefire.org/security/iecookies/showcookie.html?.amazon.com.

This hack confuses IE into thinking the page is located in the Amazon.com domain and allows the page to read the user's Amazon.com cookie. Normally, only the site that issued a cookie has permission to read data within that cookie.

According to Peacefire, all known versions of Internet Explorer for Windows 95, 98, and NT are affected. The organisation reports that IE for the Macintosh and Unix do not appear to be affected, and no version of Netscape Navigator or any other browser is vulnerable.

Peacefire says the safest workaround for Windows IE users is to disable JavaScript. When the browser loads a URL like www.peacefire.org%2fsecurity%2fiecookies%2fshowcookie.html%3F.amazon.com, the Amazon.com cookie is only available to JavaScript code on the page; it is not submitted to the server in an HTTP header.

A spokesperson for Microsoft says that the company is working on a patch for the IE cookie issue to be released shortly. A security bulletin will be published at www.microsoft.com/technet/security/default.asp to discuss the issue and advise customers how to obtain and apply the patch.

Microsoft acknowledges that the vulnerability could allow a malicious website operator to read, change, or delete cookies that belong to another site. However, according to the company, the vulnerability could not be used by a malicious website operator to "inventory" what cookies a person has. Instead, the hacker would need to randomly try to recover cookies from various sites.

However, Peacefire's Jamie McCarthy says that a number of popular sites deploy cookies that collect sensitive information. He pointed out that intercepting a cookie set by Hotmail, Yahoo Mail, or any other free Web-based email sites that use cookies for authentication could allow the operator of a hostile website to break into a visitor's Hotmail account and read the contents of the user's inbox.

McCarthy also points out that intercepting a user's Amazon.com cookie could allow a hacker to visit Amazon.com impersonating that user, and access their real name and email address. Credit card numbers or actual lists of previous Amazon.com orders can't be accessed because viewing this information requires a password not contained in the cookie, says McCarthy.

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Ann Harrison

PC World
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