Cookie data in IE may be vulnerable to snooping

Thousands of e-commerce sites use cookies to authenticate users or store private information. However, those cookies could be exposed by IE and intercepted by a third-party Web site, according to an Internet privacy watchdog group.

Seattle-based has demonstrated that by using a specially constructed URL, a Web site can read IE cookies set from any domain. For example, to read an cookie, a site might direct the user's browser to Peacefire points out that if the "%2f"'s ares replaced with "/" characters, and the "%3F" with "?", this URL is

This hack confuses IE into thinking the page is located in the domain and allows the page to read the user's 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, the cookie is only available to JavaScript code on the page; it is not submitted to the server in a Hypertext Transfer Protocol (HTTP) header.

A spokesman for Microsoft said on Friday that the company is working on a patch for the IE cookie issue to be released shortly. A security bulletin will be published at to discuss the issue and advise customers how to obtain and apply the patch. Microsoft also plans to send the bulletin via its Product Security Notification Service to more than 100,000 subscribers.

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

"Normal security practices recommend that Web sites should never include sensitive data in cookies," the spokesman said, adding that Microsoft Web sites never include sensitive data in cookies. "If these practices are followed, there would be no sensitive data to compromise."

However, Peacefire's Jamie McCarthy said 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 e-mail sites that use cookies for authentication, could allow the operator of a hostile Web site to break into a visitor's HotMail account and read the contents of the user's inbox. While HotMail cookies do not contain user passwords, they do allow a third party to access a user's HotMail account for as long as that user stays logged in, since each separate login generates a new cookie.

McCarthy also points out that the ability to harvest cookie information could be tempting for unscrupulous marketers. Intercepting a user's cookie could allow a hacker to visit impersonating that user, and access their real name, e-mail address and the user's list of "recommended titles," which could indicate past purchases of books and CDs. Credit-card numbers or actual lists of previous orders can't be accessed because viewing this information requires a password not contained in the cookie, says McCarthy.

Such a privacy hole can also be used to cull password information. For instance, McCarthy notes that some publications store passwords in cookies. While a password is only needed to browse articles on and not make purchases, exposing this password is still dangerous since users might have the same password set up for several different sites.

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