“Digital Camouflage”: The LLVM challenge in LLM-based malware detection

Large Language Models (LLMs) have emerged as promising tools for malware detection by analyzing code semantics, identifying vulnerabilities, and adapting to evolving threats. However, their reliability under adversarial compiler-level obfuscation is yet to be discovered. In this study, we empirically evaluate the robustness of three state-of-the-art LLMs: ChatGPT-4o, Gemini Flash 2.5, and Claude Sonnet 4 against compiler-level obfuscation techniques implemented via the LLVM infrastructure. These include control flow flattening, bogus control flow injection, instruction substitution, and split basic blocks, which are widely used to evade detection while preserving malicious behavior. We perform a structured evaluation on 40 C functions (20 vulnerable, 20 secure) sourced from the Devign dataset and obfuscated using LLVM passes. Our results show that these models often fail to correctly classify obfuscated code, with precision, recall, and F1-score dropping significantly after transformation. This reveals a critical limitation: LLMs, despite their language understanding capabilities, can be easily misled by compiler-based obfuscation strategies. To promote reproducibility, we release all evaluation scripts, prompts, and obfuscated code samples in a public repository. We also discuss the implications of these findings for adversarial threat modeling, and outline future directions such as software watermarking, compiler-aware defenses, and obfuscation-resilient model design. • LLMs detect vulnerabilities in clean C code with high accuracy. • Compiler-level obfuscation causes consistent misclassifications in LLMs. • LLVM IR transformations affect both vulnerable and non-vulnerable samples. • We evaluated LLMs on obfuscated code via a structured, reproducible protocol. • All code, prompts, and scripts are released for reproducibility in our Github repo and all necesarry steps are in the README file.