Hackers Could Take Control of Car Dashboard by Hacking Its Modem

Modern vehicles are increasingly defined by their connectivity, transforming them into sophisticated IoT devices on wheels. While this digital evolution enhances the driving experience, it introduces severe security risks.

A hypothetical scenario where a car dashboard is remotely hijacked to run video games like Doom has become a frightening reality.

This vulnerability stems from the integrated System-on-Chip technology used in automotive head units, specifically those combining application and communication processors to manage vehicle functions.

The core issue resides in the Unisoc UIS7862A System-on-Chip, a component widely deployed in modern vehicle head units.

This chip integrates a modem responsible for 3G, 4G, and 5G connectivity. Attackers can exploit weaknesses in this modem to gain initial entry.

Once inside, they can pivot laterally to the application processor, effectively seizing control of the dashboard’s operating system and compromising user data.

Securelist analysts identified a critical flaw in the modem’s implementation of the 3G RLC protocol.

By analyzing the firmware, they discovered that the mechanism for handling data packet fragmentation lacks sufficient bounds checking.

This oversight enables remote adversaries to execute arbitrary code on the modem processor, thereby bypassing standard cellular security measures before a secure channel is established.

The discovery highlights the fragility of “black box” components in automotive supply chains.

Exploiting the Stack-Based Buffer Overflow

The technical root of this vulnerability is a stack-based buffer overflow in the function that parses incoming Service Data Units.

The protocol allows for an unlimited number of optional headers in a packet, signaled by a specific bit value. The parsing algorithm sequentially processes these headers and writes data to a stack variable.

However, the stack depth is strictly limited to 0xB4 bytes, whereas the malicious packet size can reach up to 0x5F0 bytes.

An attacker can trigger this overflow by sending a single malformed packet with enough headers to exceed the stack buffer. Since the function lacks stack canary protection, this action overwrites the return address.

The researchers used Return-Oriented Programming techniques to bypass the non-executable stack restrictions. They constructed a ROP chain that redirected execution to the AT+SPSERVICETYPE command handler, thereby enabling them to transfer data to RAM.

// Pseudo-representation of the vulnerable parsing logic
void process_sdu_headers(packet_data *sdu) {
    uint16_t header_stack[0x5A]; // 0xB4 bytes buffer
    while (sdu->has_more_headers) {
       // Writes beyond buffer without checking bounds
       header_stack[index++] = read_next_header(); 
    }
}

By exploiting this memory corruption, the attackers executed their own code, as evidenced by patching the memory protection unit table to grant write permissions.

This access eventually enabled them to compromise the Android kernel and run arbitrary applications on the car’s head unit.

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