Which provides the highest level of security in a firewall?

Stateful inspection provides the highest level of security in a firewall because it not only examines the header information of packets but also keeps track of the state of active connections. This means that it can monitor the state and context of the traffic, allowing it to make more informed decisions about whether to allow or block certain packets based on the established connection.

By maintaining a state table, stateful firewalls can identify legitimate packets that are part of an existing connection and recognize unauthorized packets that do not fit the expected behavior. This dynamic approach to security enables stateful firewalls to respond effectively to different types of traffic and potential threats, unlike stateless filters and simple packet inspection methods. Hence, stateful inspection is considered more robust as it provides a comprehensive view of the traffic flow and context, significantly enhancing security compared to other options like outbound packet filters or stateless inspection, which focus on basic packet attributes without considering connection state.