Turns out, it may not be safe because touch screens come with touch controllers hardware attached and software installed. It is possible that these replacement parts may contain secret hardware that can hijack the security of the device. The service technician may not even be aware that the hardware being used is compromised.
In a research paper titled “Shattered Trust: When Replacement Smartphone Components Attack” and presented at the 11th USENIX Workshop on Offensive Technologies (WOOT ’17) held in Vancouver, BC, Canada, the researchers focus on how a commonly used touchscreen controller purchased from aftermarket components can be programmed to sureptitiously install malicious software, take pictures and send them via email, capture data and execute privileged operations.
Abstract: Phone touchscreens, and other similar hardware components such as orientation sensors, wireless charging controllers, and NFC readers, are often produced by third-party manufacturers and not by the phone vendors themselves. Third-party driver source code to support these components is integrated into the vendor’s source code. In contrast to “pluggable” drivers, such as USB or network drivers, the component driver’s source code implicitly assumes that the component hardware is authentic and trustworthy. As a result of this trust, very few integrity checks are performed on the communications between the component and the device’s main processor.
In this paper, we call this trust into question, considering the fact that touchscreens are often shattered and then replaced with aftermarket components of questionable origin. We analyze the operation of a commonly used touchscreen controller. We construct two standalone attacks, based on malicious touchscreen hardware, that function as building blocks toward a full attack: a series of touch injection attacks that allow the touchscreen to impersonate the user and exfiltrate data, and a buffer overflow attack that lets the attacker execute privileged operations. Combining the two building blocks, we present and evaluate a series of end-to-end attacks that can severely compromise a stock Android phone with standard firmware. Our results make the case for a hardware-based physical countermeasure.
Of course, this is just a research paper and there has not been any reported case of this happening, so there’s no need to panic if you have had your phone or tablet screen replaced recently. The pictures and videos also show large wires connecting the various phone components, but of course, these would just be etched into hardware when actually manufactured.
Now that people know it can be done and just how to do it, cell phone manufacturers need to program safeguards against this happening in their new models going forward. Old models may need a firmware fix.