Which of the following has been implemented when a host-based firewall on a legacy Linux...

A compensating control is a type of security control that is implemented in lieu of a recommended security measure that is deemed too difficult or impractical to implement at the present time. A compensating control must provide equivalent or comparable protection for the system or network and meet the intent and rigor of the original security requirement. An example of a compensating control is using a host-based firewall on a legacy Linux system to allow connections from only specific internal IP addresses, as it can provide a similar level of defense as a network firewall that may not be compatible with the system. References:

https://www.techtarget.com/whatis/definition/compensating-control

https://reciprocity.com/resources/whats-the-difference-between-compensating-controls-and-mitigating-controls/