Which type of network attack requires the attacker to have physical access to the network?

Packet sniffing as a network attack involves intercepting and analyzing packets of data being transmitted over a network. For an attacker to effectively perform packet sniffing, they typically need to be on the same local area network (LAN) as the targeted data traffic. This often requires physical access to the network or at least access to an unprotected wireless network segment. By connecting to the network, an attacker can use various sniffing tools to capture sensitive information such as usernames, passwords, and other data being transmitted.

In contrast, the other types of attacks mentioned do not necessarily require physical access. Denial-of-service attacks can be launched remotely by overwhelming a target system with traffic from various locations, while man-in-the-middle attacks can also occur without the attacker being physically present, as they can intercept communications over the internet from remote locations. Brute-force attacks, aimed at cracking passwords by systematically trying combinations, can be executed from anywhere as long as the attacker has access to the service being targeted. Therefore, packet sniffing is distinctive in that it demands physical access to the network environment to be successful.