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 further 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.