What utility monitors system logs for repeated failures from the same host?

The utility that monitors system logs for repeated failures from the same host is denyhosts. This tool is specifically designed to enhance security by preventing unauthorized access attempts from malicious hosts. It works by analyzing log files, particularly those related to SSH login attempts, to identify repeated failed login attempts from a specific IP address.

When denyhosts detects a pattern of failure from the same host, such as multiple incorrect password attempts in a short amount of time, it can take action to block that host, mitigating potential security threats. This functionality is crucial for protecting systems from brute force attacks, which often originate from the same set of IP addresses trying to guess credentials.

The other options serve different purposes:

• ipset is used to manage collections of IP addresses for firewalls, enhancing iptables.
• firewalld is a dynamic firewall management tool, providing a way to manage firewall rules without needing to restart the firewall service.
• iptables is a powerful tool for configuring firewalls in Linux, controlling traffic flow, but it does not have built-in capabilities to monitor log files for failed login attempts.

Thus, denyhosts is the correct answer as it directly addresses the need for monitoring and responding to repeated authentication failures from the same source.