Mask-Guided Hybrid Triggers for Robust Clean-Label Backdoor Attacks

Abstract

Clean-label backdoor attacks pose significant security threats to deep neural networks by injecting triggers without altering ground-truth labels. However, existing methods face a fundamental dilemma: sample-agnostic triggers are robust but easily detectable, while sample-specific triggers offer superior stealthiness but suffer from limited effectiveness due to feature suppression. To bridge this gap, we propose a new backdoor trigger framework called Mask-Guided Hybrid Trigger (MGHT). MGHT uses an adaptive mask to allocate spatial regions of the hybrid trigger between a sample-agnostic anchor for reliable memorization and a sample-specific camouflage for perceptual and semantic consistency. To prevent the optimization from greedily relying on a single trigger component, we further propose a Synergy-driven Co-optimization Strategy with a margin-based Synergy Loss. This ensures that the hybrid trigger is more effective and robust than either component alone. Extensive experiments on benchmark datasets demonstrate that MGHT achieves competitive performance, attaining over 99% ASR on CIFAR-10 and CelebA and showing strong effectiveness on higher-resolution benchmarks, while maintaining high visual quality (PSNR > 30 dB) and robustness to mainstream backdoor defenses.