@inproceedings{
su2024model,
title={Model X-ray : Detecting Backdoored Models via Decision Boundary},
author={Yanghao Su and Jie Zhang and Ting Xu and Tianwei Zhang and Weiming Zhang and Nenghai Yu},
booktitle={ACM Multimedia 2024},
year={2024},
url={https://openreview.net/forum?id=77IS5a80GK}
}
Backdoor attacks pose a significant security vulnerability for deep neural networks (DNNs), enabling them to operate normally on clean inputs but manipulate predictions when specific trigger patterns occur. In this paper, we consider a practical post-training scenario backdoor defense, where the defender aims to evaluate whether a trained model has been compromised by backdoor attacks. Currently, post-training backdoor detection approaches often operate under the assumption that the defender has knowledge of the attack information, logit output from the model, and knowledge of the model parameters, limiting their implementation in practical scenarios. In contrast, our approach functions as a lightweight diagnostic scanning tool that operates in conjunction with other defense methods, assisting in defense pipelines.

We begin by presenting an intriguing observation: the decision boundary of the backdoored model exhibits a greater degree of closeness than that of the clean model. Simultaneously, if only one single label is infected, a larger portion of the regions will be dominated by the attacked label. Leveraging this observation, drawing an analogy to X-rays in disease diagnosis, we propose Model X-ray . This novel backdoor detection approach is based on the analysis of illustrated two-dimensional (2D) decision boundaries, offering interpretability and visualization. Model X-ray can not only identify whether the target model is infected but also determine the target attacked label under the all-to-one attack strategy. Importantly, it accomplishes this solely by the predicted hard labels of clean inputs, regardless of any assumptions about attacks and prior knowledge of the training details of the model. Extensive experiments demonstrated that Model X-ray can be effective and efficient across diverse backdoor attacks, datasets, and architectures.
Model X-ray : Detecting Backdoored Models via Decision Boundary
Yanghao Su Jie Zhang Ting Xu Tianwei Zhang Weiming Zhang Nenghai Yu