Automated Essay Scoring (AES) is one of the most widely studied applications of Natural Language Processing (NLP) in education and educational measurement. Recent advances with pre-trained Transformer-based large language models (LLMs) have shifted AES from feature-based modeling to leveraging contextualized language representations. These models provide rich semantic representations that substantially improve scoring accuracy and human–machine agreement compared to systems relying on handcrafted features. However, their robustness towards adversarially crafted inputs remains poorly understood. In this study, we define adversarial input as any modification of the essay text designed to fool an automated scoring system into assigning an inflated score. We evaluate a fine-tuned DeBERTa-based AES model on such inputs and show that it is highly susceptible to a simple text duplication attack, highlighting the need to consider adversarial robustness alongside accuracy in the development of AES systems.