Seattle-based Peacefire.org 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 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 organization 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.
A spokesman for Microsoft Corp. said 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 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."
McCarthy also points out that the ability to harvest cookie information could be tempting for unscrupulous marketers. Intercepting a user's Amazon.com cookie could allow a hacker to visit Amazon.com 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 Amazon.com 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 NYTimes.com and not make purchases, exposing this password is still dangerous since users might have the same password set up for several different sites.