Final answer:
To perform passive reconnaissance and check publicly available vulnerability information for his organization's vulnerable systems, Eric can use methods like searching for his domain in Shodan, checking against the CVE database, and using the OpenVAS central vulnerability data repository.
Step-by-step explanation:
The best method for Eric to perform a passive reconnaissance and check publicly available vulnerability information for his organization's vulnerable systems would be to search for his domain in Shodan. Shodan is a search engine that allows users to find specific types of devices connected to the internet, including vulnerable systems. By searching for his domain in Shodan, Eric can identify any publicly accessible vulnerabilities associated with his organization's systems.
Additionally, checking against the CVE database for his domain would also be beneficial. The CVE database (Common Vulnerabilities and Exposures) provides a comprehensive list of publicly known cybersecurity vulnerabilities. Eric can search for his domain in the CVE database to determine if any vulnerabilities have been reported for his organization's systems.
Lastly, using the OpenVAS central vulnerability data repository would also be an effective method for performing passive reconnaissance. OpenVAS is an open source vulnerability assessment tool that helps identify known vulnerabilities in a network. Eric can leverage the central vulnerability data repository of OpenVAS to check for any reported vulnerabilities associated with his organization's systems.