Multi-Processor System-on-Chips (MPSoCs) is a standard platform used in time-critical applications. These platforms usually employ Priority-Preemptive NoCs (PP-NoCs), a widely used real-time on-chip interconnection structure that offers communication predictability. A deep analysis of the PP-NoC parameters and their impact on system security is required. Moreover, countermeasures that can protect the system while guaranteeing the real-time capabilities should be proposed and evaluated. To this end, this paper explores and evaluates the impact of the PP-NoCs parameters on system security; exploits PP-NoCs vulnerabilities and demonstrates for the first time two very powerful attacks; and proposes and integrates three new security countermeasures: RT-blinding, RT-masking, and RT-shielding. Results show that PP-NoCs are vulnerable to attacks and that is possible to uncover victim’s information with high accuracy (up to 96.19%). On the other hand, protection techniques were able to harden the system, effectively and efficiently mitigating the vulnerabilities while maintaining deterministic behavior.