Firefox is one of the most used web browsers in the world. This browser is one of the favorites for users who seek extra security and privacy and, incidentally, want to move a little away from the control exercised by Google over our digital lives. Mozilla, the company responsible for this browser, offers users good maintenance for the browser, with regular updates and security corrections. However, they always end up showing serious failures that endanger the integrity of our data, as has happened with this new failure in Firefox, a failure that has been present for more than 17 years.

A security researcher has released a serious vulnerability in Firefox that allows a hacker to steal any file from a PC using simply an HTML file. This security flaw has been demonstrated in the latest version of the browser and, according to the security researcher explains, has been present in it for more than 17 years.

How can they steal any file from our PC by uploading an HTML file in Firefox

According to the researcher who has discovered this security breach in the browser, hackers can take advantage of the way in which Mozilla implements the Same Origin Policy (SOP) feature in the browser through the file: // URI, allowing any file access other files that may be hosted in any folder or subfolder.

As SOP features are not defined in any standard, each browser implements it in different ways. Most browsers usually treat files as different sources and, therefore, websites do not have access to them. However, the implementation of Firefox is different, and Mozilla has never changed it, leading to this security breach.

In this way, if a hacker gets to trick users to download an HTML file (from a web, in an email, or sending it together with another file), make the file open with Firefox and click on a false button , the hacker could get a list with all the files and folders of the system, see the contents of any file and even send them to a remote server through HTTPS.

Of course, we must bear in mind that the malicious HTML file can only access the directory where it is located and the subfolders that are in that directory, it can not move freely through the directory tree.

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