ICSQuartz: Scan Cycle-Aware and Vendor-Agnostic Fuzzing for Industrial Control Systems

—Industrial Control Systems (ICS) ensure the automation and safe operation of critical industry, energy, and commerce processes. Despite its importance, ICS code often cannot be evaluated as rigorously as software on traditional computing platforms, as existing code evaluation tools cannot readily interface with the closed ICS ecosystem. Moreover, the use of domain-specific languages, the lack of open and extensible compilers, and the deficiency of techniques developed for ICS-specific nuances, among other challenges, hinder the creation of specialized tools. This paper addresses these challenges by introducing ICSQuartz, the first native fuzzer for IEC 61131-3 Structured Text (ST), a standardized Programmable Logic Controller (PLC) programming language. Native support eliminates the necessity of any vendor or architecture-specific requirements. ICSQuartz outperforms the fastest state-of-the-art fuzzers in the ICS space by more than an order of magnitude in executions per second . In addition to natively fuzzing ST code, we introduce novel mutation strategies to ICSQuartz that uncover vulnerabilities due to the scan cycle architecture of ST programs–a nuance that traditional fuzzers do not consider. Using ICSQuartz, we perform the first large-scale fuzzing campaign of real-world ICS libraries, resulting in multiple vulnerability disclosures and bug fixes. In addition to vulnerabilities, ICSQuartz discovered a bug in an open-source ST compiler. These findings underscore the imperative impact of ICSQuartz in the ICS domain.