New security flaw threatens Internet Explorer users

Users of Google Chrome and Apple Safari are safe

Windows users have been warned of a new security vulnerability. A January 28 security advisory issued by Microsoft stated that the company is "is investigating new public reports of a vulnerability in all supported editions of Microsoft Windows."

"The best way to think of this is to call it a variant of a cross-side scripting vulnerability," said Andrew Storms, director of security operations at nCircle Security. Cross-site scripting bugs (or XSS) can be used to insert malicious script into a Web page that can then take control of the session.

"An attacker could pretend to be the user, and act if as he was you on that specific site," said Storms. "If you were at Gmail.com or Hotmail.com, he could send e-mail as you."

A blog entry at Microsoft's Security Response Center Web site states: "For instance, an attacker could construct an HTML link designed to trigger a malicious script and somehow convince the targeted user to click it. When the user clicked that link, the malicious script would run on the user's computer for the rest of the current Internet Explorer session. Such a script might collect user information (eg., email), spoof content displayed in the browser, or otherwise interfere with the user's experience...

"The workaround we are recommending customers apply locks down the MHTML protocol and effectively addresses the issue on the client system where it exists. We are providing a Microsoft Fix-it package to further automate installation."

MHTML combines resources of several different formats -- images, Java applets, Flash animations and the like -- into a single file. Only Microsoft's IE and Opera Software's Opera support MHTML natively. Google's Chrome Web browser and Apple's Safari do not, and while Mozilla's Firefox can, it requires an add-on to read and write MHTML files.

Further reading: Microsoft warns of new Windows zero-day bug

Original report: Gregg Keizer, Computerworld US.