We constructed a newly large-scale and comprehensive C/C++ vulnerability dataset named MegaVul by crawling the Common Vulnerabilities and Exposures (CVE) database and CVE-related open-source projects. Specifically, we collected all crawlable descriptive information of the vulnerabilities from the CVE database and extracted all vulnerability-related code changes from 28 Git-based websites. We adopt advanced tools to ensure the extracted code integrality and enrich the code with four different transformed representations. Totally, MegaVul contains 17,380 vulnerabilities collected from 992 open-source repositories spanning 169 different vulnerability types disclosed from January 2006 to October 2023. Thus, MegaVul can be used for a variety of software security-related tasks including detecting vulnerabilities and assessing vulnerability severity. All information is stored in the JSON format for easy usage. MegaVul is publicly available on GitHub and will be continuously updated. It can be easily extended to other programming languages.

Previous studies have been conducted on software vulnerability (SV) assessment at the code-based level, especially the function level. However, a key limitation of these studies is that they do not consider the structure information (e.g., control dependency and data dependency) of a vulnerable function, which is crucial for understanding SVs and assigning priority for fixing. In this study, we propose a flow-sensitive, multitask, and function-level vulnerability assessment method named FVA, which considers both global structure information and local semantic information. More specifically, FVA considers two types of flow information extracted from the control dependence graph and the data dependence graph. Meanwhile, FVA also considers the deep semantic information of the statement as well as its various types of contexts (i.e., surrounding context and program slicing context). We evaluate the effectiveness of FVA on the large-scale dataset (4,467 functions) by comparing it with four state-of-the-art baselines in terms of five performance measures. The experimental results indicate that FVA outperforms these baselines by a significant margin. More precisely, on average, FVA obtains 0.795 of F1-score and 0.727 of MCC, which improves baselines by 5%-14% and 8%-20%, respectively.