Microsoft investigates new Internet Explorer flaw

Microsoft said on Wednesday that it is investigating another flaw in Internet Explorer, this time a vulnerability that could result in an unauthorized disclosure of information for users running its browser on older operating systems.

The software maker said in a security advisory that, although it knows of no attacks based on the flaw, the vulnerability could lead to a Web-based attack from either a Web site designed to take advantage of the flaw or from a site that becomes compromised via user-generated text or a malicious ad. Either way, a user would have to actively go to the compromised Web site.

The flaw is separate from the one used to attack Google and other companies, which Microsoft addressed with an "out-of-band" security update last month.

The latest flaw could affect those running Windows XP and Internet Explorer on Windows XP. The software maker said those running the browser on a machine running Windows Vista or Windows 7 aren't vulnerable because the browser runs in a "protected mode" by default.

McAfee spokesman Joris Evers said that, although the latest issue doesn't allow the attacker to gain full control of a system, it nonetheless represents "a serious vulnerability that can expose personal information or system information that may be used in a follow up attack."

"Internet Explorer users should ensure they are protected against exploitation of this flaw and apply the patch when Microsoft releases it," Evers said.

Microsoft said it may take additional action when it finishes its inquiry, such as releasing an update as part of its monthly "Patch Tuesday" or as part of a special, out-of-band update. In the mean time, the software maker offered an automated "Fix It" that can turn on the protected mode for those running IE 6.