What type of attack involves an attacker inserting themselves into communications between two parties?

The correct answer is Man-in-the-Middle (MITM) because this type of attack specifically describes a scenario in which an attacker intercepts and potentially alters the communication between two legitimate parties without their knowledge. In a MITM attack, the attacker establishes a connection with both parties, effectively positioning themselves in the middle of the communication channel. This enables the attacker to monitor, capture, and manipulate data being transmitted, which can lead to various malicious outcomes such as data theft or unauthorized changes to the messages exchanged.

Other types of attacks mentioned, such as packet sniffing, focus on the passive interception of data packets without actively altering the communication. Phishing attacks target users directly to trick them into revealing sensitive information, and session hijacking refers to taking over an active session after it has already been established. While these attacks can be harmful, they do not involve the same direct insertion into the communication process as a MITM attack does. Therefore, Man-in-the-Middle is distinctively characterized by the proactive involvement of the attacker in the ongoing communication between two parties.