Context Matters – From Single ECU to Full Vehicle Pentesting

In our previous blog, we explored the Cyber Resilience Act (CRA) and its direct impact on individual Electronic Control Units (ECUs). Building on that foundation, this article highlights the differences between single-ECU testing, functional ECU cluster assessments, and full vehicle pentesting. Each layer introduces unique challenges and attack surfaces – and requires tailored penetration testing strategies.

Single ECU Testing: Isolated but Regulatory-Critical

A single ECU – such as an engine control unit or airbag controller – is a well-defined target for penetration testing. Communication protocols and exposed interfaces can be tested in isolation. However, testing a component outside of its vehicle context has limitations: many security-relevant functions only emerge when multiple ECUs interact.

Despite this limitation, single ECU testing remains vital. The CRA (EU 2024/2847) is a horizontal regulation applying to products with digital elements from Dec 11, 2027. It does not single out ECUs explicitly, but ECUs can fall under its scope. In automotive, UNECE R155 and R156 obligations apply in parallel.

Cluster ECU Testing: Functional Groups with Broader Attack Surfaces

Modern vehicles are built from functional ECU clusters rather than standalone units. For example, a drivetrain cluster includes motor, transmission, and energy management ECUs, while an infotainment cluster integrates head units, displays, and connectivity modules.

This interconnectedness increases complexity:

• Attack vectors emerge from the internal communication between ECUs.
• Platform technologies e.g. Volkswagen’s MIB (Modular Infotainment Toolkit) or Hyundai’s E-GMP (Electric Global Modular Platform) enable re-use of hardware and software architectures. While efficient, this also means a single vulnerability can propagate across multiple models.

Cluster testing therefore bridges the gap between isolated ECU validation and full vehicle testing, revealing security issues that arise in real-world integration.

Full Vehicle Pentesting: Essential for Homologation

At the top level, the entire vehicle must be validated as part of the homologation process. Regulatory frameworks such as UNECE R155 demand comprehensive cybersecurity risk management, ensuring that not just components, but the complete vehicle, is protected.

Full vehicle penetration testing examines critical interfaces such as:

• OBD connectors accessible to consumers or workshops (Accessibility is limited by gateways/ segmentation; not all ECUs are exposed over OBD).
• Wireless interfaces like FOTA (Flashing Over the Air), Bluetooth, or LTE,
• Backend integrations, which are now deeply embedded in modern vehicle architectures.

Only by testing the vehicle as a fully integrated system – including ECUs, clusters, and platform technologies – can OEMs realistically simulate attacks and assess resilience.

Technical Dimensions of Automotive Pentesting

Beyond organizational and regulatory aspects, technical interfaces play a decisive role in penetration testing:

• Physical interfaces like OBD ports or debug connectors remain classic entry points.
• Wireless interfaces (WiFi, LTE, BLE, UWB) extend the attack surface beyond physical access.
• Backend systems are integral parts of the modern vehicle ecosystem. Full vehicle cybersecurity testing must include backend and cloud integrations.
• SOTA processes, which are usually orchestrated through coordinated backend systems, are especially critical. UNECE R156/SUMS requires integrity, rollback/recovery options, and sufficient power supply for safe updates.

Organizational & Economic Aspects

Cybersecurity testing always balances cost, effort, and development timing:

• Cost & effort: Single ECU tests are relatively fast and inexpensive, while full vehicle tests are resource-intensive and logistically complex.
• Timing: ECU pentests make sense early in the development phase. Cluster testing becomes most effective during integration. Full vehicle cybersecurity testing represents the final hardening step, required for type approval and regulatory compliance.

A seamless transition between these levels is crucial. An ECU can first be tested in isolation, then validated within a cluster of interconnected units, and finally as part of the complete vehicle. The full vehicle combines different clusters (or modular platforms), which together form the vehicle architecture across an entire generation.

It is also important to note that not all ECUs are equally accessible in the vehicle context. Some cannot be reached via the OBD interface and may lack a diagnostic stack altogether. These ECUs still require dedicated testing — although they are the exception rather than the rule.

From an organizational perspective, ECUs are usually developed and supplied by tier-1 or tier-2 vendors. Clusters or modular platforms are often defined early in pre-development, while the overall vehicle is coordinated by a dedicated vehicle integrator. The OEM ultimately provides the overarching requirements that align the different levels of testing.

Conclusion: HydraVision as a Bridge Across the Lifecycle

Automotive cybersecurity cannot be reduced to a single level of testing. ECUs, clusters, and full vehicles each pose different challenges, and only their combination delivers a realistic view of resilience against cyberattacks. While individual pentests provide valuable insights, many risks only emerge when components interact within the vehicle and its extended ecosystem.

The challenge is cost: full vehicle cybersecurity testing is expensive and complex. This is where HydraVision provides a decisive advantage. By enabling continuous monitoring across ECUs, clusters, and complete platforms, HydraVision extends security validation beyond the testing phase into the entire security lifecycle.

• OEMs and suppliers gain real-time transparency into the security status of their systems,
• vulnerabilities can be identified and addressed early via secure updates,
• and the cost of repeated, large-scale vehicle tests is significantly reduced.

In this way, HydraVision turns penetration testing into ongoing assurance. It complements regulatory frameworks like CRA and UNECE R155 by helping manufacturers meet and maintain compliance — while also delivering lasting value through reduced costs and greater resilience.