Microsoft’s Internet Explorer has a longstanding reputation for poor security, but it’s now bad enough that you could be attacked just by having it on your PC. Security researcher John Page has revealed an unpatched exploit in the web browser’s handling of MHT files (IE’s web archive format) that hackers can use to both spy on Windows users and steal their local data. As Windows opens MHT files using IE by default, you don’t even have to run the browser for this to be a problem — all you have to do is open an attachment sent through chat or email.

The vulnerability affects Windows 7, Windows 10 and Windows Server 2012 R2.

This wouldn’t be an issue if it weren’t for the disclosure of the flaw. Page posted details of the exploit after Microsoft reportedly declined to roll out an urgent security fix. It instead said a fix would be “considered” in a future release. While that does suggest a patch is on the way, it leaves millions of users potentially vulnerable unless they either turn off Internet Explorer or point to another app that can open MHT files.

Source: ZDNet