Adversarially Robust Assembly Language Model for Packed Executables Detection

Abstract: Detecting packed executables is a critical component of large-scale malware analysis and antivirus engine workflows, as it identifies samples that warrant computationally intensive dynamic unpacking to reveal concealed malicious behavior. Traditionally, packer detection techniques have relied on empirical features, such as high entropy or specific binary patterns. However, these empirical, feature-based methods are increasingly vulnerable to evasion by adversarial samples or unknown packers (e.g., low-entropy packers). Furthermore, the dependence on expert-crafted features poses challenges in sustaining and evolving these methods over time. In this paper, we examine the limitations of existing packer detection methods and propose Pack-ALM, a novel deep-learning-based approach for detecting packed executables. Inspired by the linguistic concept of distinguishing between real and pseudo words, we reformulate packer detection as a task of differentiating between legitimate and "pseudo" instructions. To achieve this, we preprocess native data and packed data into "pseudo" instructions and design a pre-trained assembly LLM that recognizes features indicative of packed data. We evaluate Pack-ALM against leading industrial packer detection tools and state-of-the-art assembly LLMs. Extensive experiments on over 37,000 samples demonstrate that Pack-ALM effectively identifies packed binaries, including samples created with adversarial or previously unseen packing techniques. Moreover, Pack-ALM outperforms traditional entropy-based methods and advanced assembly LLMs in both detection accuracy and adversarial robustness.