Restoring the system from a known good backup is the most appropriate eradication method when responding to an incident resulting in malware on an application server, as it ensures that the system is free of any malicious code and that the data and applications are consistent with the expected state. Disconnecting the system from the network may prevent further spread of the malware, but it does not eradicate it from the system. Changing passwords on the compromised system may reduce the risk of unauthorized access, but it does not remove the malware from the system. Performing operation system hardening may improve the security configuration of the system, but it does not guarantee that the malware is eliminated from the system.
References = CISM Review Manual 2022, page 3131; CISM Exam Content Outline, Domain 4, Task 4.4