CVE-2018-18203 in StarLink Harman Head Unit
Summary
by MITRE
A vulnerability in the update mechanism of Subaru StarLink Harman head units 2017, 2018, and 2019 may give an attacker (with physical access to the vehicle's USB ports) the ability to rewrite the firmware of the head unit. This occurs because the device accepts modified QNX6 filesystem images (as long as the attacker obtains access to certain Harman decryption/encryption code) as a consequence of a bug where unsigned images pass a validity check. An attacker could potentially install persistent malicious head unit firmware and execute arbitrary code as the root user.
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Analysis
by VulDB Data Team • 04/16/2020
The vulnerability identified as CVE-2018-18203 represents a critical security flaw in Subaru StarLink Harman head units manufactured between 2017 and 2019, specifically targeting the firmware update mechanism that operates on QNX6 operating system. This weakness stems from insufficient validation procedures within the device's update process, creating an exploitable condition that allows attackers with physical access to vehicle USB ports to manipulate the system's firmware. The vulnerability operates under CWE-284 which classifies it as an improper access control issue, specifically involving inadequate validation of firmware images during the update process. The attack vector requires physical proximity to the vehicle, leveraging the USB port as an entry point, which aligns with the ATT&CK framework's T1059.001 technique for command and scripting interpreter, though in this case the execution occurs at the firmware level rather than through traditional software interfaces.
The technical implementation of this vulnerability exploits a fundamental flaw in the firmware validation logic where unsigned QNX6 filesystem images bypass the authenticity checks that should normally prevent unauthorized modifications. The system accepts modified filesystem images without proper cryptographic verification, creating a pathway for attackers who possess access to Harman's specific decryption and encryption code. This code access requirement represents a significant operational limitation for attackers, as it necessitates either reverse engineering the encryption mechanisms or obtaining the proprietary keys through other means. The vulnerability's design flaw allows unsigned firmware images to pass validity checks, which constitutes a failure in the cryptographic integrity verification process and directly relates to CWE-327, which addresses the use of weak or broken cryptographic algorithms.
The operational impact of this vulnerability extends far beyond simple unauthorized firmware modification, as it enables attackers to install persistent malicious firmware that can survive system reboots and maintain control over the vehicle's infotainment system. The ability to execute arbitrary code as the root user represents a complete compromise of the system's security model, allowing attackers to potentially access all system resources and data. This persistent threat capability means that even after the vehicle is powered off and restarted, the malicious firmware remains active, creating a long-term security risk for vehicle owners. The root privilege execution allows for complete system control, including potential access to vehicle communication protocols and other connected systems, which aligns with ATT&CK's T1543.003 technique for creating or modifying system level executable.
Mitigation strategies for this vulnerability require multiple layers of protection to address both the physical access and software exploitation aspects. Vehicle owners should implement strict physical security measures to prevent unauthorized access to USB ports, including physical locks or covers that prevent unauthorized connection of external devices. System administrators and security teams should consider disabling USB ports when not actively needed for diagnostics or updates, and implement firmware integrity monitoring systems that can detect unauthorized modifications to the system. The vulnerability highlights the importance of proper cryptographic validation and secure boot processes, which should be implemented using strong encryption algorithms and proper key management practices as recommended by NIST SP 800-155. Additionally, regular security assessments of automotive infotainment systems should be conducted to identify similar validation flaws in other vehicle components, particularly those utilizing QNX operating systems or similar embedded platforms that may be susceptible to similar attacks.