Common Vulnerabilities and Exposures (CVE) is the correct answer because it is a database that provides a reference-method for publicly known information-security vulnerabilities and exposures. The CVE system provides a unique identifier to each security vulnerability, making it an essential source for penetration testers to identify potential threats. On the other hand, CWE provides a common language for describing software security weaknesses, Shodan is a search engine for Internet-connected devices, and Recon-ng is a full-featured web reconnaissance framework.