Polar: Function Code Aware Fuzz Testing of ICS Protocol

Industrial Control System (ICS) protocols are widely used to build communications among system components. Compared with common internet protocols, ICS protocols have more control over remote devices by carrying a specific field called “function code”, which assigns what the receive end should do. Therefore, it is of vital importance to ensure their correctness. However, traditional vulnerability detection techniques such as fuzz testing are challenged by the increasing complexity of these diverse ICS protocols. In this paper, we present a function code aware fuzzing framework — Polar, which automatically extracts semantic information from the ICS protocol and utilizes this information to accelerate security vulnerability detection. Based on static analysis and dynamic taint analysis, Polar initiates the values of the function code field and identifies some vulnerable operations. Then, novel semantic aware mutation and selection strategies are designed to optimize the fuzzing procedure. For evaluation, we implement Polar on top of two popular fuzzers — AFL and AFLFast, and conduct experiments on several widely used ICS protocols such as Modbus, IEC104, and IEC 61850. Results show that, compared with AFL and AFLFast, Polar  achieves the same code coverage and bug detection numbers at the speed of 1.5X-12X. It also gains increase with 0%--91% more paths within 24 hours. Furthermore, Polar has exposed 10 previously unknown vulnerabilities in those protocols, 6 of which have been assigned unique CVE identifiers in the US National Vulnerability Database.