A host-based firewall controls incoming and outgoing network traffic on a device by enforcing security rules, effectively blocking unwanted or insecure communications. It is specifically designed to protect the device from unauthorized access and malicious traffic.

System hardening (A) reduces vulnerabilities by disabling unnecessary services and patching but does not control communications dynamically. Intrusion detection systems (C) detect suspicious traffic but typically do not block it (unless paired with prevention). Anti-malware (D) protects against malicious software but not directly network communication filtering.

Host-based firewalls are a fundamental component of endpoint security highlighted in the Security Operations domain of SY0-701【6:Chapter 11†CompTIA Security+ Study Guide】.