We report competitive results on RobustBench for CIFAR and SVHN using a simple yet effective baseline approach. Our approach involves a training protocol that integrates rescaled square loss, cyclic learning rates, and erasing-based data augmentation. The outcomes we have achieved are comparable to those of the model trained with state-of-the-art techniques, which is currently the predominant choice for adversarial training. Our baseline, referred to as SimpleAT, yields three novel empirical insights. (i) By switching to square loss, the accuracy is comparable to that obtained by using both de-facto training protocol plus data augmentation. (ii) One cyclic learning rate is a good scheduler, which can effectively reduce the risk of robust overfitting. (iii) Employing rescaled square loss during model training can yield a favorable balance between adversarial and natural accuracy. In general, our experimental results show that SimpleAT effectively mitigates robust overfitting and consistently achieves the best performance at the end of training. For example, on CIFAR-10 with ResNet-18, SimpleAT achieves approximately 52% adversarial accuracy against the current strong AutoAttack. Furthermore, SimpleAT exhibits robust performance on various image corruptions, including those commonly found in CIFAR-10-C dataset. Finally, we assess the effectiveness of these insights through two techniques: bias-variance analysis and logit penalty methods. Our findings demonstrate that all of these simple techniques are capable of reducing the variance of model predictions, which is regarded as the primary contributor to robust overfitting. In addition, our analysis also uncovers connections with various advanced state-of-the-art methods.

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