A security analyst suspects a remote server is running vulnerable network applications. The analyst does not have administrative credentials for the server. Which of the following would MOST likely help the analyst determine if the applications are running?

A port scanner is a software application designed to probe a server or host for open ports. Network applications and services listen on specific ports to receive incoming connections. By scanning a remote server's ports, an analyst can identify which ports are open, which directly corresponds to the services or applications that are running and accessible over the network. This method is a fundamental reconnaissance technique that does not require any administrative credentials on the target server, making it the most suitable tool for the analyst's task.

A. User account control: This is a security component of the Windows operating system that operates locally on the server and cannot be accessed or queried remotely without credentials.
B. Anti-malware: This is software that runs on the target server to detect threats. The analyst, being remote and without credentials, cannot run or view reports from this software.
C. A sniffer: A sniffer passively captures network traffic. It would only reveal running applications if they were actively communicating and the sniffer was positioned to intercept that specific traffic.

1. Fyodor (Gordon Lyon). (2023). Nmap Reference Guide. Nmap.org. In the "Introduction" section, it states, "Nmap (“Network Mapper”) is a free and open source utility for network discovery and security auditing... It uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running...". This directly supports using a port scanner (Nmap) to determine running services.

2. Frans Kaashoek, Nickolai Zeldovich. (2014). 6.858 Computer Systems Security, Fall 2014. Massachusetts Institute of Technology: MIT OpenCourseWare. In Lecture 12: Network Security, Slide 11, "Reconnaissance," nmap is listed as the primary tool to "Find open ports, identify services" on a target machine.

3. Shaukat, S. K., & Masood, A. (2017). A survey on port scanning techniques. Egyptian Informatics Journal, 18(2), 107-115. The abstract states, "Port scanning is one of the most popular reconnaissance techniques attackers use to discover services they can break into. It is normally a prelude to an attack and it is therefore important to detect and prevent it." This academic source establishes port scanning as the standard method for discovering services. DOI: https://doi.org/10.1016/j.eij.2016.10.001.

4. Raluca Ada Popa. (2020). CS 161: Computer Security, Spring 2020. University of California, Berkeley. In Lecture 15: Network Security I, the section "Finding Vulnerable Hosts" describes port scanning as the method to "find out what services are running on a machine" by checking which ports are open.