Vendor cybersecurity risk assessment is of critical importance to smart city infrastructure and sustainability of the autonomous mobility ecosystem. Lack of engagement in cybersecurity policies and process implementation by the tier companies providing hardware or services to OEMs within this ecosystem poses a significant risk to not only the individual companies but to the ecosystem overall. The proposed quantitative method of estimating cybersecurity risk allows vendors to have visibility to the financial risk associated with potential threats and to consequently allocate adequate resources to cybersecurity. It facilitates faster implementation of defense measures and provides a useful tool in the vendor selection process. The paper focuses on cybersecurity risk assessment as a critical part of the overall company mission to create a sustainable structure for maintaining cybersecurity health. Compound cybersecurity risk and impact on company operations as outputs of this quantitative analysis present a unique opportunity to strategically plan and make informed decisions towards acquiring a reputable position in a sustainable ecosystem. This method provides attack trees and assigns a risk factor to each vendor thus offering a competitive advantage and an insight into the supply chain risk map. This is an innovative way to look at vendor cybersecurity posture. Through a selection of unique industry specific parameters and a modular approach, this risk assessment model can be employed as a tool to navigate the supply base and prevent significant financial cost. It generates synergies within the connected vehicle ecosystem leading to a safe and sustainable economy.