It seems something always happens when Microsoft tries a new security feature. According to Broken Browser, this time it’s the Microsoft Edge browser, the default browser in Windows 10, which can be tricked into issuing fake alerts.

Spoofing Microsoft Edge

SmartScreen is an Edge subprogram designed to keep users off malware-distributing sites. As quoted by Softpedia, “SmartScreen checks the sites you visit against a dynamic list of reported phishing sites and malicious software sites. If it finds a match, SmartScreen will show you a warning letting you know that the site has been blocked for your safety.”

To do this, Edge locally maintains a dynamic list of bad URLs. If a user types in a blacklisted URL, the browser will not load the resource. Instead, it displays a message alerting the user that the content has been blocked.

This is where fraudsters try to sneak in, attempting to display their own image instead of the legitimate alert screen.

Current Windows apps use the protocols ms-appx: and ms-appx-web: to load internal resources. This is how Edge accesses the BlockSite list it needs to consult. But the protocols will also load other pages if those pages are correctly specified, which can lead to trouble.

One could call window.open to create a new window and populate it with resources used by the BlockSite page. An impostor would look just like the legitimate BlockSite. Of course, the cybercriminals could also specify false information and populate the page with whatever they wanted.

A security researcher did just that. Along with a cheesy telephone support scam banner that he wrote, he showed how a telephone number could be inserted into such a window. Not only that, but Edge was ready to place the call for the victim.

Remote Possibilities?

It gets better: The researcher was also able to spoof Edge into showing that social media giant Facebook was an unsafe website just by including different code in the window.open statement.

Just because someone can pull this off on a local machine doesn’t prove that this kind of thing can be done remotely. But it does raise the question of whether such an attack vector is possible. Fortunately, Windows 10 gets updated regularly. That will help ensure that this and similar situations are dealt with in a timely manner.