Which of the following attacks aims to make a service unavailable by overwhelming it with traffic?

The Denial of Service (DoS) attack is specifically designed to make a service unavailable by overwhelming it with an excessive amount of traffic or requests. This overwhelming effect can exhaust system resources, causing legitimate users to be unable to access the service or application. In a typical DoS attack scenario, the attacker sends a flood of traffic to the target server, which cannot handle the volumetric load, leading to service disruption.

In contrast, the other types of attacks listed do not focus on service availability. A man-in-the-middle attack focuses on intercepting and potentially altering communications between two parties. Cross-site scripting is a type of vulnerability exploitation where an attacker injects malicious scripts into web pages viewed by others. Phishing attacks aim to deceive individuals into providing sensitive information through fake communications. Therefore, none of these alternatives directly relate to the goal of disrupting service availability, making Denial of Service the accurate choice.