TL;DR
A security researcher has demonstrated a vulnerability in Honda Civic headunits that allows physical attackers, such as valet drivers, to install malicious updates via USB. This could enable unauthorized control over vehicle systems. The attack, termed ‘Evil Valet’, exploits the headunit’s update process, raising security concerns for vehicle owners.
A security researcher has revealed a critical vulnerability in Honda Civic headunits that enables physical attackers to install malicious software via USB updates, without requiring root access. This development raises concerns about vehicle security, especially in scenarios involving valet services or other physical access points.
The researcher, who conducted reverse engineering of the 2021 Honda Civic headunit, confirmed that the update process relies on a signed AOSP update file, which is signed with a publicly-known test key. As a result, anyone with physical access to the vehicle and knowledge of the update process can craft and install arbitrary code on the headunit by formatting a USB drive with a signed update file.
This attack, dubbed ‘Evil Valet’ by the researcher, mimics an ‘evil maid’ attack but in a vehicle context, where a valet driver or other malicious actor with physical access can modify the car’s headunit without detection. The attacker can potentially gain arbitrary code execution, which could lead to control over vehicle functions or installation of malicious software.
The researcher also developed a tool called ota-builder, which simplifies creating update files that the headunit will accept, further lowering the barrier for malicious actors. While the researcher has not confirmed whether all Honda headunits are vulnerable, the evidence suggests that many models using similar update mechanisms are susceptible.
Implications for Vehicle Security and Owner Safety
This vulnerability highlights a significant security flaw in Honda Civics’ headunits, which could be exploited in real-world scenarios such as valet theft, carjacking, or malicious tampering. Since the attack requires only physical access and the ability to connect a USB device, it presents a practical threat for vehicle owners and fleet operators. The potential for remote or automated exploitation underscores the need for automakers to review and strengthen their update security protocols.
In the broader context, this case exemplifies risks associated with in-car infotainment systems that rely on signed updates without sufficient validation or security measures, raising questions about the security standards across connected vehicles.

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Background on Honda Headunit Security and Reverse Engineering Efforts
Three years ago, the researcher began reverse engineering the headunit of a 2021 Honda Civic, focusing on the update process. They discovered that Honda’s update mechanism involves signing files with a publicly-known AOSP test key, which can be exploited to install malicious code if physical access is available. This finding aligns with broader concerns in automotive cybersecurity about in-car system vulnerabilities.
Previous research has documented similar issues in other vehicle models, but this is among the first publicly detailed exploits targeting Honda Civics specifically. The researcher has developed tools to analyze and modify update files, enabling further exploration of the vulnerability and potential exploits.
“As long as someone has physical access to the USB port and can craft a signed update, they can install arbitrary code on the headunit.”
— Researcher

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Remaining Questions About Scope and Mitigation
It is not yet clear how widespread the vulnerability is across all Honda Civic models or other Honda vehicles. The researcher believes many headunits share similar update mechanisms, but confirmation is ongoing. Honda has not publicly commented on the vulnerability or whether they plan to issue security updates or patches. The effectiveness of potential mitigations, such as improved update validation or hardware protections, remains to be seen.

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Next Steps for Honda and Vehicle Owners
Automakers like Honda are expected to review the vulnerability and consider security patches or updates for affected models. Vehicle owners are advised to limit physical access to their cars’ USB ports and monitor official channels for security advisories. The researcher plans to continue developing tools and sharing findings to help improve automotive cybersecurity and assist owners in assessing their vehicles’ security risks.

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Key Questions
Can this vulnerability be exploited remotely?
No. The attack requires physical access to the vehicle’s USB port, so it cannot be exploited remotely without physical access.
Does this affect all Honda Civics?
The vulnerability appears to be present in models that use the same update signing process, but confirmation across all variants is ongoing. Honda has not officially confirmed the scope.
What can vehicle owners do to protect themselves?
Owners should restrict physical access to their vehicle’s USB ports and be cautious when handing over their cars to valet services or other third parties. Monitoring for official security updates is also recommended.
Will Honda issue a security patch?
There has been no official statement from Honda regarding patches. It is uncertain whether they will address the vulnerability in upcoming updates.
Source: Hacker News