Browser-in-the-browser attacks: from theory to reality

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A browser-in-the-browser attack, theoretically described in 2022, has been adopted in real-world phishing. We break down how it works, and how to spot a fake authentication window.

 
In 2022, we dived deep into an attack method called browser-in-the-browser — originally developed by the cybersecurity researcher known as mr.d0x. Back then, no actual examples existed of this model being used in the wild. Fast-forward four years, and browser-in-the-browser attacks have graduated from the theoretical to the real: attackers are now using them in the field. In this post, we revisit what exactly a browser-in-the-browser attack is, show how hackers are deploying it, and, most importantly, explain how to keep yourself from becoming its next victim.

What is a browser-in-the-browser (BitB) attack?

For starters, let’s refresh our memories on what mr.d0x actually cooked up. The core of the attack stems from his observation of just how advanced modern web development tools — HTML, CSS, JavaScript, and the like — have become. It’s this realization that inspired the researcher to come up with a particularly elaborate phishing model.

A browser-in-the-browser attack is a sophisticated form of phishing that uses web design to craft fraudulent websites imitating login windows for well-known services like Microsoft, Google, Facebook, or Apple that look just like the real thing. The researcher’s concept involves an attacker building a legitimate-looking site to lure in victims. Once there, users can’t leave comments or make purchases unless they “sign in” first.

Signing in seems easy enough: just click the Sign in with {popular service name} button. And this is where things get interesting: instead of a genuine authentication page provided by the legitimate service, the user gets a fake form rendered inside the malicious site, looking exactly like… a browser pop-up. Furthermore, the address bar in the pop-up, also rendered by the attackers, displays a perfectly legitimate URL. Even a close inspection won’t reveal the trick.

From there, the unsuspecting user enters their credentials for Microsoft, Google, Facebook, or Apple into this rendered window, and those details go straight to the cybercriminals. For a while this scheme remained a theoretical experiment by the security researcher. Now — real-world attackers have added it to their arsenals.

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