Software-defined vehicles (SDVs) operate in dynamic cyber-physical environments where vehicle motion, sensor performance, network conditions and computational load influence system behavior. Consequently, static laboratory and bench testing alone is insufficient to fully assess cybersecurity resilience. Real-world operating conditions, including varying speeds, perception uncertainty, environmental noise and communication latency, can expose vulnerabilities that remain hidden in controlled environments and may become safety critical during operation. The growing use of over-the-air (OTA) updates increases complexity by introducing continuous changes to perception, decision-making and control functions. Dynamic cybersecurity validation addresses these challenges by assessing security controls during real-world operation, ensuring their effectiveness across evolving conditions and software updates.