GhostTouch: how to remotely control touchscreens with EMI

Security researchers devised a technique, dubbed GhostTouch, to remotely control touchscreens using electromagnetic signals.

A team of researchers from Zhejiang University and Technical University of Darmstadt devised a technique, dubbed GhostTouch, to remotely control capacitive touchscreens using electromagnetic signals.

According to the experts, GhostTouch is the first active contactless attack against capacitive touchscreens.

GhostTouch uses electromagnetic interference (EMI) to remotely inject fake touch points into a capacitive device. The researchers demonstrated how to inject two types of basic touch events, taps and swipes, into targeted locations of the touchscreen. The events allowed the researchers to control the devices (i.e. answering an eavesdropping phone call, pressing the button, swiping up to unlock), the attack technique was successful on nine smartphone models.

“We can inject targeted taps continuously with a standard deviation of as low as 14.6 x 19.2 pixels from the target area, a delay of less than 0.5s and a distance of up to 40mm. We show the real-world impact of the GhostTouch attacks in a few proof-of-concept scenarios, including answering an eavesdropping phone call, pressing the button, swiping up to unlock, and entering a password.” reads the research paper published by the academics. “Finally, we discuss potential hardware and software countermeasures to mitigate the attack.”

The GhostTouch system consists of two components, a touch injector and a phone locator. The touch injector is used to inject touch events into the touchscreen and includes a signal generator, an amplifier, an on/off switch, and a receiving antenna array. The phone locator is used to identify the position of the touchscreen and consists of a sensing antenna array, a data acquisition device, and a location calculator.

The experimental lab setup up by the researchers is composed of an electrostatic gun used to generate a strong pulse signal which is sent to an antenna to transmit an electromagnetic field to the touchscreen.

Below are a couple of video PoCs of attacks devised by the experts that show GhostTouch attack to answer the phone call and connect the malicious Bluetooth.

The experts tested the technique against nine different smartphone models, including Galaxy A10s, Huawei P30 Lite, Honor View 10, Galaxy S20 FE 5G, Nexus 5X, Redmi Note 9S, Nokia 7.2, Redmi 8, and an iPhone SE (2020).

“We demonstrate the feasibility of this attack in the real world.” concludes the paper. “In places like a cafe, library, meeting room, or conference lobbies, people might place their smartphone face-down on the table2. An attacker may embed the attack equipment under the table and launch attacks remotely. For example, an attacker may impersonate the victim to answer a phone call which would eavesdrop the private conversation, or visit a malicious website.”

The researchers provided a series of countermeasures to neutralize the attack, including adding electromagnetic shielding to block EMI, reinforcing the touchscreen, improving the detection algorithm of the touchscreen, and forcing some form of authentication for the execution of high-risk actions.

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Pierluigi Paganini

(SecurityAffairs – hacking, GhostTouch)