A novel phishing technique called browser-in-the-browser (BitB) attack can be exploited to simulate a browser window within the browser in order to spoof a legitimate domain, thereby making it possible to stage convincing phishing attacks.
According to penetration tester and security researcher, who goes by the handle mrd0x on Twitter, the method takes advantage of third-party single sign-on (SSO) options embedded on websites such as “Sign in with Google” (or Facebook, Apple, or Microsoft).
While the default behaviour when users attempt to log in using these methods is for them to receive a pop up window, BitB attempts to duplicate this process by using a combination of HTML and CSS codes to make a completely fabricated browser window.
Interestingly, the technique has been abused in the wild at least once before. In February 2020, Zscaler disclosed details of a campaign that leveraged the BitB trick to siphon credentials for video game digital distribution service Steam by means of fake Counter-Strike: Global Offensive (CS: GO) websites.
” Normally, a user must check to verify that the URL is genuine, whether it is HTTPS enabled, and whether any homographs are present in the domain,” Prakhar Shrotriya, a Zscaler researcher, stated at the time.
“In this case, everything looks fine as the domain is steamcommunity[.]com, which is legitimate and is using HTTPS. But when we try to drag this prompt from the currently used window, it disappears beyond the edge of the window as it is not a legitimate browser pop-up and is created using HTML in the current window. “
While this method significantly makes it easier to mount effective social engineering campaigns, it’s worth noting that potential victims need to be redirected to a phishing domain that can display such a fake authentication window for credential harvesting.
“But once landed on the attacker-owned website, the user will be at ease as they type their credentials away on what appears to be the legitimate website (because the trustworthy URL says so),” mrd0x added.