One of the guiding principles of open source software development is to use crowds of developers to keep a watchful eye on source code. Eric Raymond declared Linus' Law as "many eyes make all bugs shallow", with the socio-technical argument that high quality open source software emerges when developers combine together their collective experience and expertise to review code collaboratively. Vulnerabilities are a particularly nasty set of bugs that can be rare, difficult to reproduce, and require specialized skills to recognize. Does Linus' Law apply to vulnerabilities empirically? In this study, we analyzed 159,254 code reviews, 185,948 Git commits, and 667 post-release vulnerabilities in the Chromium browser project. We formulated, collected, and analyzed various metrics related to Linus' Law to explore the connection between collaborative reviews and vulnerabilities that were missed by the review process. Our statistical association results showed that source code files reviewed by more developers are, counter-intuitively, more likely to be vulnerable (even after accounting for file size). However, files are less likely to be vulnerable if they were reviewed by developers who had experience participating on prior vulnerability-fixing reviews. The results indicate that lack of security experience and lack of collaborator familiarity are key risk factors in considering Linus' Law with vulnerabilities.

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