ATAC: Augmentation-Based Test-Time Adversarial Correction for CLIP

Linxiang Su; András Balogh

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arXiv · 2511.17362

ATAC: Augmentation-Based Test-Time Adversarial Correction for CLIP

Linxiang Su·András Balogh

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Abstract

Despite its remarkable success in zero-shot image-text matching, CLIP remains highly vulnerable to adversarial perturbations on images. As adversarial fine-tuning is prohibitively costly, recent works explore various test-time defense strategies; however, these approaches still exhibit limited robustness. In this work, we revisit this problem and propose a simple yet effective strategy: Augmentation-based Test-time Adversarial Correction (ATAC). Our method operates directly in the embedding space of CLIP, calculating augmentation-induced drift vectors to infer a semantic recovery direction and correcting the embedding based on the angular consistency of these latent drifts. Across a wide range of benchmarks, ATAC consistently achieves remarkably high robustness, surpassing that of previous state-of-the-art methods by nearly 50\% on average, all while requiring minimal computational overhead. Furthermore, ATAC retains state-of-the-art robustness in unconventional and extreme settings and even achieves nontrivial robustness against adaptive attacks. Our results demonstrate that ATAC is an efficient method in a novel paradigm for test-time adversarial defenses in the embedding space of CLIP. Code is available at: https://github.com/kylin0421/ATAC

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Linxiang Su, András Balogh. 2025-11-21. ATAC: Augmentation-Based Test-Time Adversarial Correction for CLIP. https://arxiv.org/abs/2511.17362

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