Which of the following is NOT one of the firewall management challenges?

Cost efficiency is not typically categorized as a firewall management challenge in the same vein as management complexity, misconfigured policies, and slow response. In the context of firewall management, challenges are generally focused on operational issues that directly affect the effectiveness and security of the firewall.

Management complexity refers to the intricate tasks of configuring and maintaining firewalls, especially within environments that have multiple firewalls or complicated rule sets. Misconfigured policies highlight the risks associated with poorly defined firewall rules that can lead to security vulnerabilities. Slow response points to the potential delays in incident response due to inefficient management or lack of resources.

Cost efficiency, while an essential consideration for overall IT budgeting and resource allocation, is not a direct challenge that impacts the daily management and operational workflow of firewalls. Instead, it's more of a broader business objective that may influence decisions about firewall solutions rather than a challenge directly related to managing the firewall itself.