Software Vulnerabilities (SVs) can expose software systems to cyber-attacks, potentially causing enormous financial and reputational damage for organizations. There have been significant research efforts to detect these SVs so that developers can promptly fix them. However, fixing SVs is complex and time-consuming in practice, and thus developers usually do not have sufficient time and resources to fix all SVs at once. As a result, developers often need SV information, such as exploitability, impact, and overall severity, to prioritize fixing more critical SVs. Such information required for fixing planning and prioritization is typically provided in the SV assessment step of the SV lifecycle. Recently, data-driven methods have been increasingly proposed to automate SV assessment tasks. However, there are still numerous shortcomings with the existing studies on data-driven SV assessment that would hinder their application in practice. This PhD thesis aims to contribute to the growing literature in data-driven SV assessment by investigating and addressing the constant changes in SV data as well as the lacking considerations of source code and developers’ needs for SV assessment that impede the practical applicability of the field. Particularly, we have made the following five contributions in this thesis. (1) We systematize the knowledge of data-driven SV assessment to reveal the best practices of the field and the main challenges affecting its application in practice. Subsequently, we propose various solutions to tackle these challenges to better support the real-world applications of data-driven SV assessment. (2) We first demonstrate the existence of the concept drift (changing data) issue in descriptions of SV reports that current studies have mostly used for predicting the Common Vulnerability Scoring System (CVSS) metrics. We augment report-level SV assessment models with subwords of terms extracted from SV descriptions to help the models more effectively capture the semantics of ever-increasing SVs. (3) We also identify that SV reports are usually released after SV fixing. Thus, we propose using vulnerable code to enable earlier SV assessment without waiting for SV reports. We are the first to use Machine Learning techniques to predict CVSS metrics on the function level leveraging vulnerable statements directly causing SVs and their context in code functions. The performance of our function-level SV assessment models is promising, opening up research opportunities in this new direction. (4) To facilitate continuous integration of software code nowadays, we present a novel deep multi-task learning model, DeepCVA, to simultaneously and efficiently predict multiple CVSS assessment metrics on the commit level, specifically using vulnerability-contributing commits. DeepCVA is the first work that enables practitioners to perform SV assessment as soon as vulnerable changes are added to a codebase, supporting just-in-time prioritization of SV fixing. (5) Besides code artifacts produced from a software project of interest, SV assessment tasks can also benefit from SV crowdsourcing information on developer Question and Answer (Q&A) websites. We automatically retrieve large-scale security/SVrelated posts from these Q&A websites. We then apply a topic modeling technique on these posts to distill developers’ real-world SV concerns that can be used for data-driven SV assessment. Overall, we believe that this thesis has provided evidence-based knowledge and useful guidelines for researchers and practitioners to automate SV assessment using data-driven approaches.Thesis (Ph.D.) -- University of Adelaide, School of Computer Science, 202
