Which of the following tools best helps in determining service vulnerabilities during a penetration test?

The best tool for determining service vulnerabilities during a penetration test is the vulnerability scanner. This type of tool is specifically designed to identify security weaknesses and vulnerabilities in systems and applications. Vulnerability scanners can automate the process of checking for known vulnerabilities by comparing the systems against databases of vulnerabilities and exploit techniques. This ensures a comprehensive assessment can be performed in a relatively short time, highlighting issues such as unpatched software, misconfigurations, and default settings that might expose the system to threats.

In contrast, while a port scanner is useful for discovering open ports and services running on a target system, it does not assess the security of those services. A network sniffer captures and analyzes data packets on a network, which can provide insights into traffic patterns but does not directly assess the vulnerabilities of services. Similarly, a web application firewall serves to protect web applications by filtering and monitoring HTTP traffic, but it does not evaluate the vulnerabilities present within services. Thus, while each of these tools has its place in a penetration testing toolkit, the vulnerability scanner stands out as the most effective for identifying service vulnerabilities.