Microsoft's new browser haunted by old flaw

A security problem originally found in Microsoft Corp.'s Internet Explorer 6 browser has returned to haunt IE7, the new version of the browser launched two weeks ago, a security consultant said Monday.

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Danish security consultancy Secunia AsP posted an advisory regarding an issue where an attacker could potentially snare logins and passwords from an unsuspecting IE7 user. Over two years ago, security researchers reported the same fault in IE6.

If a user visits a Web site specially crafted by an attacker, and then opens a "trusted" site such as a bank or e-commerce site that has a pop-up window, the attacker can put new content into the pop-up, said Thomas Kristensen, Secunia's chief technology officer. This could enable the attacker to ask a user for financial information or passwords, he said.

When the problem was revealed in June 2004, Microsoft gave instructions for a workaround for IE6: disable the setting "Navigate sub-frames across different domains." That setting is disabled by default in IE7, but does not appear to prevent the attack, Kristensen said.

Microsoft has been notified of the flaw, which was submitted to Secunia by a user, Kristensen said. Microsoft officials did not have an immediate comment on Monday morning.

Secunia rated the problem as "moderately critical," but Kristensen said the company was not aware of sites trying to exploit the flaw.

An alert user might notice that they're under attack: Since the URL (uniform resource locator) for the pop-up window is visible, it may be possible to identify a fraudulent request for password information, for example. But "it would require you to pay some attention to the address bar," Kristensen said.

However, a clever attacker could also use this problem in combination with a pop-up spoofing weakness identified last week. Microsoft hasn't patched that problem.

Following IE7's release on Oct. 18, Secunia found a problem it shared with IE6. The vulnerability allowed an attacker to potentially read information from a secure Web site if the user had also opened a maliciously crafted Web site. Microsoft said that the problem is actually in code called by the browsers in another application, Outlook Express, which remains unpatched.