Title: Flareon: Stealthy Backdoor Injection via Poisoned Augmentation. Abstract: Open software supply chain attacks, once successful, can exact heavy costs in mission-critical applications.  As open-source ecosystems for deep learning flourish and become increasingly universal, they present attackers previously unexplored avenues to code-inject malicious backdoors in deep neural network models.  This paper proposes Flareon, a simple, stealthy, mostly-free, and yet effective backdoor injection payload that specifically targets the data augmentation pipeline with motion-based triggers.  Flareon neither alters ground-truth labels, nor modifies the training loss objective, nor does it assume prior knowledge of the victim model architecture and training hyperparameters.  By learning multiple triggers for targets simultaneously, it can even produce models that learn target-conditional (or ``any2any'') backdoors.  Model trained under Flareon exhibits higher attack success rates for any target choices and better clean accuracies than competing attacks that not only seize greater capabilities, but also assume more restrictive attack targets.  We also demonstrate the effectiveness of Flareon against recent defenses.  Flareon is fully open-source and available online to the deep learning community.