A reboot loop is a failure state where a device crashes during startup, restarts automatically, and never reaches normal operation. Instead of becoming usable, it cycles through boot, fault, and restart again and again. This can happen on servers, firewalls, gateways, phones, and other appliances when firmware, drivers, configuration, or a software update triggers a fatal error early in the boot process.
In cyber security, reboot loops matter because they can turn a protective system into an outage. A perimeter gateway in a reboot loop may block remote access, break authentication, or interrupt traffic inspection, leaving defenders to balance availability against exposure. Attackers can also cause reboot loops indirectly by exploiting bugs, sending malformed inputs, or forcing resource exhaustion. For defenders, the practical response is staged patching, rollback planning, and monitoring for repeated restarts after changes.