Exploit code for one of the vulnerabilities is publicly available presents the greatest concern because it means that anyone can easily exploit the vulnerability and compromise the web application. This increases the risk of data breach, denial of service, or other malicious attacks. Therefore, exploit code for one of the vulnerabilities is publicly available is the correct answer.
References:
https://www.imperva.com/learn/application-security/penetration-testing/
https://www.netspi.com/blog/technical/web-application-penetration-testing/are-you-testing-your-web- application-for-vulnerabilities/