File systems have been developed for decades with the securitycritical foundation provided by operating systems. However, they are still vulnerable to malware attacks and software defects. In this paper, we undertake the first attempt to systematically understand the security vulnerabilities in various file systems. We conduct an empirical study of 157 real cases reported in Common Vulnerabilities and Exposures (CVE). We characterize the file system vulnerabilities in different dimensions that include the common vulnerabilities leveraged by adversaries to initiate their attacks, their exploitation procedures, root causes, consequences, and mitigation approaches. We believe the insights derived from this study have broad implications related to the further enhancement of the security aspect of file systems, and the associated vulnerability detection tools.