Fixing of Security Vulnerabilities in Open Source Projects: A Case Study of Apache HTTP Server and Apache Tomcat

Software vulnerabilities are particularly dangerous bugs that may allow an attacker to violate the confidentiality, integrity or availability constraints of a software system. Fixing vulnerabilities soon is of primary importance; besides, it is crucial to release complete patches that do not leave any corner case not covered. In this paper we study the process of vulnerability fixing in Open Source Software. We focus on three dimensions: personal, i.e., who fixes software vulnerabilities; temporal, i.e., how long does it take to release a patch; procedural, i.e., what is the process followed to fix the vulnerability. In the context of our study we analyzed 337 CVE Entries regarding Apache HTTP Server and Apache Tomcat and we manually linked them to the patches written to fix such vulnerabilities and their related commits. The results show that developers who fix software vulnerabilities are much more experienced than the average. Furthermore, we observed that the vulnerabilities are fixed through more than a commit and, surprisingly, that in about 3% of the cases such vulnerabilities show up again in future releases (i.e., they are not actually fixed). In the light of such results, we derived some lessons learned that represent a starting point for future research directions aiming at better supporting developers during the documentation and fixing of vulnerabilities.