SquareX discovered a Fullscreen BitM attack targeting Safari users, exploiting Fullscreen API vulnerabilities to steal credentials.BitM attacks involve tricking victims by displaying genuine login pages in a pop-up window to steal sensitive information.SquareX's research exposed a major Safari-specific flaw in the Fullscreen API, allowing for more convincing attacks.Safari users are at higher risk due to no clear visual indication when entering fullscreen mode.The use of Fullscreen API in combination with BitM enables attackers to create convincing fake login pages.Other browsers like Firefox and Chrome have subtle notifications for fullscreen mode, while Safari lacks this feature.Existing security solutions struggle to detect Fullscreen BitM attacks due to architectural limitations.Security researchers advise enterprises to update defense strategies against advanced browser attacks.SquareX's Browser Detection and Response tool helps organizations detect and mitigate web-based threats effectively.The Fullscreen BitM Attack disclosure is part of a series focusing on browser security by SquareX's research team.