CVE-2017-14937 in Car
Summary
by MITRE
The airbag detonation algorithm allows injury to passenger-car occupants via predictable Security Access (SA) data to the internal CAN bus (or the OBD connector). This affects the airbag control units (aka pyrotechnical control units or PCUs) of unspecified passenger vehicles manufactured in 2014 or later, when the ignition is on and the speed is less than 6 km/h. Specifically, there are only 256 possible key pairs, and authentication attempts have no rate limit. In addition, at least one manufacturer's interpretation of the ISO 26021 standard is that it must be possible to calculate the key directly (i.e., the other 255 key pairs must not be used). Exploitation would typically involve an attacker who has already gained access to the CAN bus, and sends a crafted Unified Diagnostic Service (UDS) message to detonate the pyrotechnical charges, resulting in the same passenger-injury risks as in any airbag deployment.
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Analysis
by VulDB Data Team • 11/27/2019
The vulnerability described in CVE-2017-14937 represents a critical security flaw in automotive airbag control systems that fundamentally compromises occupant safety through predictable authentication mechanisms. This issue affects passenger vehicles manufactured from 2014 onwards and specifically targets the airbag control units or pyrotechnical control units (PCUs) that manage airbag deployment. The flaw becomes exploitable when the vehicle ignition is on and the vehicle speed is below 6 kilometers per hour, creating a dangerous operational window where unauthorized airbag deployment becomes possible. The vulnerability stems from a fundamental design weakness in the security access protocol implementation that allows attackers to predict and manipulate authentication data through a limited key space of only 256 possible key pairs, a design choice that directly violates established security principles for automotive systems.
The technical implementation of this vulnerability demonstrates a severe lack of proper cryptographic security measures and access control mechanisms within the vehicle's internal communication protocols. The absence of rate limiting on authentication attempts creates an environment where brute force attacks can succeed with minimal effort, as the limited key space of 256 possibilities makes the system susceptible to exhaustive key search attacks. Furthermore, the interpretation of ISO 26021 standard by at least one manufacturer appears to have been misapplied, as the standard requires that all possible key pairs be utilized rather than allowing direct calculation of keys, which represents a clear deviation from established automotive cybersecurity practices. This misinterpretation effectively reduces the security of the system from a 256-bit key space to a 1-bit key space, where the correct key can be determined through direct mathematical calculation rather than through proper authentication mechanisms.
The operational impact of this vulnerability extends far beyond simple security concerns, as it directly threatens passenger safety through the potential for unauthorized airbag deployment. The ability to send crafted Unified Diagnostic Service (UDS) messages over the CAN bus to trigger pyrotechnical charges creates a real-world scenario where malicious actors could cause airbag deployment during normal driving conditions, potentially resulting in injuries to passengers and occupants. This risk is particularly concerning because airbag deployment occurs at high velocity and pressure, creating physical danger to vehicle occupants. The vulnerability's exploitation requires only basic access to the vehicle's CAN bus, which can be achieved through various means including OBD connector access or other diagnostic interfaces, making the attack surface more accessible than initially apparent. This represents a significant deviation from the expected security model where airbag systems should only deploy under specific, verified emergency conditions.
The implications of this vulnerability align with several cybersecurity frameworks and attack patterns, including those documented in the ATT&CK framework where automotive systems are categorized under the "Network Service Scanning" and "Exploitation for Privilege Escalation" domains. The vulnerability also corresponds to CWE-310, which addresses Cryptographic Issues, and CWE-305, which covers Authentication Issues, as the system fails to implement proper cryptographic key management and authentication mechanisms. Additionally, this vulnerability demonstrates characteristics of the automotive cybersecurity threat landscape that has been increasingly documented by organizations such as the SAE International and ISO standards bodies, which emphasize the need for robust security measures in automotive systems. The lack of proper security access controls and the predictable nature of the key generation process make this vulnerability particularly dangerous as it requires minimal expertise to exploit, potentially enabling even non-technical attackers to compromise vehicle safety systems and create hazardous situations for passengers.
Mitigation strategies for this vulnerability must address both the immediate security concerns and the fundamental design flaws in the authentication system. Vehicle manufacturers should implement proper rate limiting mechanisms on authentication attempts to prevent brute force attacks, while also ensuring that all possible key pairs are utilized according to established standards rather than allowing direct key calculation. The implementation of stronger cryptographic protocols and proper key management systems would be essential to prevent unauthorized access to the airbag control systems. Additionally, network segmentation and access controls should be implemented to limit access to the CAN bus to authorized diagnostic tools and systems only. Regular security assessments and updates to automotive cybersecurity protocols are necessary to prevent similar issues from emerging in future vehicle designs, and manufacturers should consider implementing security-by-design principles that incorporate proper authentication mechanisms from the earliest stages of vehicle development to ensure that safety-critical systems maintain their integrity and protect vehicle occupants from unauthorized access.