Malicious RIS Versus Massive MIMO: Securing Multiple Access Against RIS-Based Jamming Attacks

In this letter, we study an attack that leverages a reconfigurable intelligent surface (RIS) to induce harmful interference toward multiple users in massive multiple-input multiple-output (mMIMO) systems during the data transmission phase. We propose an efficient and flexible weighted-sum projected gradient-based algorithm for the attacker to optimize the RIS reflection coefficients without knowing legitimate user channels. Simulation results demonstrate that our malicious algorithm outperforms baseline strategies while offering adaptability for targeting specific users. To counter such a threat, we propose two reception strategies, which we show to be effective even if only an imperfect estimate of the cascade RIS channel is available.