WIGHT: Wired Ghost Touch Attack on Capacitive Touchscreens

The security of capacitive touchscreens is crucial since they have become the primary human-machine interface on smart devices. To the best of our knowledge, this paper presents WIGHT, the first wired attack that creates ghost touches on capacitive touchscreens via charging cables, and can manipulate the victim devices with undesired consequences, e.g., allowing malicious Bluetooth connections, accepting files with viruses, etc. Our study calls for attention to a new threat vector against touchscreens that only requires connecting to a malicious charging port, which could be a public charging station, and is effective across various power adapters and even USB data blockers. Despite the fact that smartphones employ abundant noise reduction and voltage management techniques, we manage to inject carefully crafted signals that can induce ghost touches within a chosen range. The underlying principle is to inject common-mode noises over the power line to avoid being effectively filtered yet affect the touch measurement mechanism, and synchronize the malicious noise with the screen measurement scanning cycles to place the ghost touches at target locations. We achieve three types of attacks: injection attacks that create ghost touches without users touching the screen, alteration attacks that change the detected legitimate touch position, and Denial-of-Service attacks that prevent the device from identifying legitimate touches. Our evaluation on 6 smartphones, 1 tablet, 2 standalone touchscreen panels, 6 power adapters, and 13 charging cables demonstrates the feasibility of all three type attacks.