How Insecure API Design Turned a Dealer Portal into a Vehicle Control Panel

TLDR: A recent security research project uncovered a critical vulnerability in an automotive dealer management system that allowed for unauthorized account creation and privilege escalation. By exploiting a hidden registration form and manipulating API responses, the researcher gained national-level administrative access to the platform. This access enabled the remote control of vehicles, including starting engines and tracking locations, as well as the exfiltration of sensitive customer and employee PII.

Automotive security is often discussed in the context of CAN bus injection or sophisticated radio frequency attacks, but the most dangerous vulnerabilities are frequently found in the mundane web applications that connect these vehicles to the internet. When a dealer management system is built on top of legacy AngularJS and Java backends, the attack surface is often far larger than the developers realize. The recent research presented at DEF CON 33 highlights exactly how a lack of server-side validation can turn a simple dealer portal into a remote control for thousands of vehicles.

The Vulnerability: Hidden Forms and Broken Access Control

The core of the issue was a classic case of Broken Access Control combined with insufficient server-side validation. The dealer portal was designed to be invite-only, meaning there was no public registration page. However, the registration form was not actually removed from the application; it was simply hidden from the UI using CSS.

By using Chrome DevTools to change the display property of the hidden registration element to block, the researcher was able to interact with the form directly. The application performed a client-side check to validate an invite token, but the server-side API failed to verify that the token was legitimate before processing the registration request.

The researcher discovered that by submitting a blank token in the POST request, the server would process the registration anyway. This allowed for the creation of a new account without any authorization. While the initial account had limited permissions, it provided a foothold into the internal network.

Privilege Escalation via API Manipulation

Once the researcher had a valid account, the next step was to escalate privileges. The application had a "Profile Update" feature that, when triggered, established a session via a JSESSIONID cookie. This session was the key to accessing the rest of the application.

The researcher found that the application was riddled with internal scripts and APIs that were not properly protected. By patching the frontend JavaScript to bypass error messages and redirect logic, the researcher was able to access the administrative user management interface. This interface allowed for the creation of new users with arbitrary access rights.

By checking every box in the "Access Rights" section, the researcher was able to create a new account with national-level administrative privileges. This account had access to every dealer in the system, allowing for the management of inventory, the viewing of customer PII, and, most critically, the ability to pair the account with any vehicle in the system.

Real-World Impact: From Data Exfiltration to Vehicle Control

The impact of this vulnerability is difficult to overstate. With national-level administrative access, an attacker could:

• Exfiltrate PII: Accessing the finance portal allowed for the download of thousands of PDF contracts containing sensitive customer information, including driver's license numbers, insurance policy details, and home addresses.
• Control Vehicles: The dealer management system was integrated with the vehicle's telematics platform. By pairing an administrative account with a vehicle's VIN, the attacker could use the official mobile app to remotely start the engine, unlock the doors, and track the vehicle's real-time location.
• Manipulate Inventory: The attacker could order cars, cancel shipments, and alter the balance sheets of dealerships across the country, causing significant financial and operational disruption.

For a pentester or bug bounty hunter, this research serves as a reminder that the most critical bugs are often found in the business logic of the application. When testing these types of systems, focus on the APIs that are used for administrative tasks. Look for hidden endpoints, insecure direct object references, and, most importantly, verify that the server is performing the same checks that the client is performing.

Defensive Strategies for Interconnected Systems

The primary takeaway for defenders is that server-side validation is non-negotiable. Never rely on the frontend to enforce security policies. If a form is hidden, it should be removed from the codebase entirely, not just hidden with CSS. Furthermore, all API endpoints must be protected by robust authentication and authorization checks, regardless of whether they are intended for public or internal use.

The use of Certificate Transparency logs is also a powerful tool for discovering the subdomains and APIs that make up a large attack surface. By monitoring these logs, security teams can identify new or forgotten assets before an attacker does.

The automotive industry is rapidly moving toward a model where every vehicle is a connected device. As these systems become more interconnected, the security of the backend infrastructure becomes just as important as the security of the vehicle itself. If you are working on these systems, assume that every API endpoint will be discovered and tested by an attacker. Build your security with that assumption in mind.