Which of the following services would pose the GREATEST risk when used to permit access to and from the Internet?

Exposing Remote Desktop Protocol (RDP) to the internet poses the greatest risk because it provides direct, interactive administrative access to a system's desktop. This makes it a high-value target for attackers who can use brute-force attacks, credential stuffing, or exploit vulnerabilities (like BlueKeep) to gain complete control over the machine. A successful RDP compromise can lead to data theft, ransomware deployment, or lateral movement within the network. The other services, while having their own risks, do not typically offer this level of direct system control.

A. SMB is a local network file-sharing protocol. Exposing it to the internet is extremely dangerous but less common and often blocked by ISPs.
B. FTP is risky due to cleartext credential transmission, but it provides limited file system access, not full remote control of the operating system.
C. DNS is a fundamental internet service. While it can be abused for DDoS amplification or spoofing, it does not grant direct access or control over a system.

1. Cybersecurity and Infrastructure Security Agency (CISA). (2020). Alert (AA20-073A): Enterprise VPN Security. CISA.gov. The alert specifically warns about the risks of exposing RDP to the internet for remote access.

2. Hogganvik, I., & Stølen, K. (2006). A Graphical Approach to Risk Identification, Motivated by a Case Study from the Offshore Oil and Gas Industry. In Computer Safety, Reliability, and Security (pp. 207-220). Springer. (Discusses risk assessment principles applicable to identifying high-impact threats like exposed RDP). DOI: 10.1007/1187556717