Which of the following is used by attackers to obtain an authenticated connection on a network?

A Denial-of-Service attack floods a target to disrupt availability, not to establish an authenticated connection.

A replay attack works by intercepting a legitimate, authenticated session token or credential exchange and retransmitting it to the target system. Because the replayed data is indistinguishable from a genuine authentication event, the network grants the attacker an authenticated connection. This technique bypasses the need to crack passwords since the attacker reuses already-valid session material.

A man-in-the-middle attack positions the attacker between two parties to intercept or alter traffic, but it does not specifically replay captured credentials to obtain a new authenticated session.

A back door is a hidden access mechanism planted in a system, not a technique for capturing and reusing another user's authenticated session.