God Mode On: how we attacked a vehicle’s head unit modem

[harlan4096]

Introduction

Imagine you’re cruising down the highway in your brand-new electric car. All of a sudden, the massive multimedia display fills with Doom, the iconic 3D shooter game. It completely replaces the navigation map or the controls menu, and you realize someone is playing it remotely right now. This is not a dream or an overactive imagination – we’ve demonstrated that it’s a perfectly realistic scenario in today’s world.

The internet of things now plays a significant role in the modern world. Not only are smartphones and laptops connected to the network, but also factories, cars, trains, and even airplanes. Most of the time, connectivity is provided via 3G/4G/5G mobile data networks using modems installed in these vehicles and devices.

These modems are increasingly integrated into a System-on-Chip (SoC), which uses a Communication Processor (CP) and an Application Processor (AP) to perform multiple functions simultaneously. A general-purpose operating system such as Android can run on the AP, while the CP, which handles communication with the mobile network, typically runs on a dedicated OS. The interaction between the AP, CP, and RAM within the SoC at the microarchitecture level is a “black box” known only to the manufacturer – even though the security of the entire SoC depends on it.

Bypassing 3G/LTE security mechanisms is generally considered a purely academic challenge because a secure communication channel is established when a user device (User Equipment, UE) connects to a cellular base station (Evolved Node B, eNB). Even if someone can bypass its security mechanisms, discover a vulnerability in the modem, and execute their own code on it, this is unlikely to compromise the device’s business logic. This logic (for example, user applications, browser history, calls, and SMS on a smartphone) resides on the AP and is presumably not accessible from the modem.

To find out, if that is true, we conducted a security assessment of a modern SoC, Unisoc UIS7862A, which features an integrated 2G/3G/4G modem. This SoC can be found in various mobile devices by multiple vendors or, more interestingly, in the head units of modern Chinese vehicles, which are becoming increasingly common on the roads. The head unit is one of a car’s key components, and a breach of its information security poses a threat to road safety, as well as the confidentiality of user data.

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