Low-Rank and Sparsity Are All You Need: Exploring Robust Hierarchical Latent Subspaces for Transferable Adversarial Attack

Adversarial examples pose serious threats to deep neural networks (DNNs), revealing fundamental vulnerabilities in model robustness. However, most existing adversarial attacks directly manipulate densely activated and highly redundant feature representations, which often leads to overfitting on surrogate models and poor black-box transferability. Recent SVD-based attack attempts to exploit low-rank feature subspaces, yet its reliance on single-layer optimization and single-gradient pathway neglects both structural redundancy in feature representations and hierarchical heterogeneity across network layers. To address these limitations, we propose LRS-Attack, a Low-Rank and Sparse decomposition based adversarial attack that explicitly models robust hierarchical subspaces in latent feature spaces.Specifically, the low-rank component captures dominant semantic directions, while the sparse component models localized and highly sensitive discriminative patterns. To efficiently extract low-rank structure while preserving subspace quality, we develop a Warm-started Alternating Low-rank Approximation (WALA) algorithm. Furthermore, we design a hierarchical mixture of robust experts that models depth-dependent feature characteristics and guides gradient optimization toward more transferable adversarial directions. Extensive experiments on ImageNet demonstrate that the proposed LRS-Attack consistently improves black-box adversarial transferability over state-of-the-art methods across diverse CNN/ViT architectures and defense settings.