Autonomous vehicles rely on LiDAR based perception to support safety critical control functions such as adaptive cruise control and automatic emergency braking. While previous research has shown that LiDAR perception can be manipulated through object based spoofing and injection attacks, the impact of such attacks on vehicle safety controllers is still not well understood. This paper presents a systematic failure analysis of longitudinal safety controllers under object based LiDAR attacks in highway driving scenarios. The study focuses on realistic cut in and car following situations in which adversarial objects introduce persistent perception errors without directly modifying vehicle control software. A high fidelity simulation framework integrating LiDAR perception, object tracking, and closed loop vehicle control is used to evaluate how false and displaced object detections propagate through the perception planning and control pipeline. The results demonstrate that even short duration LiDAR induced object hallucinations can trigger unsafe braking, delayed responses to real hazards, and unstable control behavior. In cut in scenarios, a clear increase in unsafe deceleration events and time to collision violations is observed when compared to benign conditions, despite identical controller parameters. The analysis further shows that controller failures are more strongly influenced by the temporal consistency of spoofed objects than by spatial inaccuracies alone. These findings reveal a critical gap between perception robustness and control level safety guarantees in autonomous driving systems. By explicitly characterizing safety controller failure modes under adversarial perception, this work provides practical insights for the design of attack aware safety mechanisms and more resilient control strategies for LiDAR dependent autonomous vehicles.