Making the Best of Both Worlds: Universal Perturbations for Live Black-Box Evasion Against NIDS in Encrypted Traffic

Abstract

Evasion attacks pose a significant threat to Network Intrusion Detection Systems (NIDS) by manipulating packets to bypass their defensive strategies. This paper presents a novel black-box evasion attack framework, BlackSlit, tailored against NIDS for encrypted traffic. Unlike traditional “buffer-and-perturb” pipelines that incur significant latency, BlackSlit enables live evasion by generating universal perturbations for incoming encrypted traffic without prior knowledge. To ensure practical applicability, BlackSlit generates packet-level perturbation sequences and imposes manipulability constraints on encrypted packet features, ensuring that the perturbations are executable at the packet level. BlackSlit comprises two core components, the Generator and the Simulator, which operate in a complementary manner. The Generator iteratively produces packet-level universal perturbations, while the Simulator mimics the behavior of black-box target NIDS to guide the update process of the Generator. Both components employ a hierarchical time-series Transformer (TST)-based architecture to account for temporal correlations intrinsic to encrypted traffic, aligning with the focus of state-of-the-art (SOTA) NIDS. This architecture ensures that temporal dependencies are effectively modeled during both perturbation generation and target system simulation, thereby enhancing the overall efficacy of evasion attacks. Evaluations are conducted on 3 real-world datasets, benchmarked against 6 leading evasion attack baselines and 9 NIDS. Results demonstrate that BlackSlit consistently outperforms state-of-the-art methods across all benchmarks. Moreover, experiments against defended NIDS confirm that BlackSlit maintains robustness.