SigUnder: a stealthy 5G low power attack and defenses

The 3GPP 5G cellular system is hailed as a major step towards more ubiquitous and pervasive communications infrastructure (including for V2X, Smart Grid, and Healthcare). We disclose and evaluate SigUnder, an attack that enables an adversary to overshadow the Signal Synchronization Block (SSB) with an injected signal at 3.4dB below the legitimate signal (prior work required 3dB above). The attack exploits the polar coding mechanism of 5G and the physical layer OFDM structure. It can be used to make previous DoS and over-shadowing attacks lower-power and stealthy, but also enables new attacks unique to 5G such as setting the cellBarred field in the 5G MIB (and blocking access to a cell). We develop techniques (e.g., phase prediction) to make the attack feasible in a practical setup, and evaluate its performance both in simulations and over the air experiments. We also introduce SICUnder, an extension of Successive Interference Cancellation (SIC) to be able to address the unique challenges that SigUnder poses and demonstrate it effectiveness relatively to standard SIC.