通过解耦任务,精准清除模型后门且几乎不损失正常性能。
Backdoor Unlearning by Linear Task Decomposition
- 将后门与正常任务在权重空间中分离,针对性消除后门影响。
- 已知攻击时可实现近似完美去毒,干净准确率仍保持96%以上。
- 无需重训练,适用于已知或未知攻击,适合部署后安全加固。
基础模型在计算机视觉中实现了跨任务的广泛泛化,但对对抗扰动和定向后门攻击仍高度敏感。现有防御方法依赖昂贵的微调来消除有害行为,常导致其他无关任务性能下降。本文研究后门在模型权重空间中的编码方式,发现其与良性任务可解耦。基于此,提出一种简单无须重训练的去毒方法,能仅移除后门影响而最小化对正常任务的影响。在基于CLIP的模型上,使用常见对抗性触发器进行实验,结果表明:当已知攻击时,该方法可实现近似完美的去毒,平均保留96%以上的干净准确率;即使攻击未知,也能通过逆向工程触发器有效识别并清除后门。相比现有最先进防御方案,本方法在去毒效果与干净性能之间取得了更优平衡。
原文摘要 · Abstract (English)
Foundation models have revolutionized computer vision by enabling broad generalization across diverse tasks. Yet, they remain highly susceptible to adversarial perturbations and targeted backdoor attacks. Mitigating such vulnerabilities remains an open challenge, especially given that the large-scale nature of the models prohibits retraining to ensure safety. Existing backdoor removal approaches rely on costly fine-tuning to override the harmful behavior, and can often degrade performance on other unrelated tasks. This raises the question of whether backdoors can be removed without compromising the general capabilities of the models. In this work, we address this question and study how backdoors are encoded in the model weight space, finding that they are disentangled from other benign tasks. Specifically, this separation enables the isolation and erasure of the backdoor's influence on the model with minimal impact on clean performance. Building on this insight, we introduce a simple unlearning method that leverages such disentanglement. Through extensive experiments with CLIP-based models and common adversarial triggers, we show that, given the knowledge of the attack, our method achieves approximately perfect unlearning, while retaining, on average, 96% of clean accuracy. Additionally, we demonstrate that even when the attack and its presence are unknown, our method successfully unlearns backdoors by proper estimation using reverse-engineered triggers. Overall, our method consistently yields better unlearning and clean accuracy tradeoffs when compared to present state-of-the-art defenses.
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