Smart Contract Vulnerability Detection Based on AST-Augmented Heterogeneous Graphs

Smart contracts have been increasingly deployed and applied on various blockchain platforms. Nevertheless, vulnerabilities may cause significant financial losses due to the involvement of substantial funds in smart contracts. Traditional analysis tools heavily rely on manually predefined rules. Recent studies have demonstrated the promising potential of deep learning techniques in smart contract vulnerability detection. However, existing approaches often disregard cross-function and cross-contract vulnerability scenarios, focusing primarily on characterization or detection tasks at the function level. In this study, we propose CL-HGAN, a novel framework for smart contract vulnerability detection at the contract level. Firstly, we construct a contract-level heterogeneous graph to embody the relationships between contracts and functions. Specifically, we build the backbone of the heterogeneous graph based on the abstract syntax tree (AST) and multiple types of edges and then incorporate two additional categories of edges to augment its structural information. Subsequently, we design a two-phase feature learning method to automatically generate graph-level representations based on a heterogeneous graph attention network and meta-paths specific to the constructed graph. Finally, we employ a classifier to perform vulnerability detection tasks. In particular, the proposed CL-HGAN comprehensively captures vulnerability features and accurately identifies vulnerabilities at the contract level. Furthermore, we evaluate the CL-HGAN framework on an Ethereum smart contract dataset containing thirty types of vulnerabilities. The experimental results show that the average metrics of our approach outperform the state-of-the-art baselines.