Denial-of-service (DoS) is an attack outcome where a system, service, or application becomes unavailable to legitimate users. The attacker may crash the process, force it into an error loop, or consume CPU, memory, network, or file descriptors until normal work cannot continue.
In cyber security, DoS matters because availability is a core part of security, especially for databases and authentication services. A flaw that stalls connection handling, replication, or query processing can interrupt applications even if data is not stolen. In real attacks, DoS often comes from malformed requests, oversized inputs, repeated handshake attempts, or protocol edge cases that trigger resource exhaustion. Defenders reduce the risk by patching vulnerable software, limiting request rates, isolating exposed services, and monitoring for spikes in errors, latency, or resource use. In PostgreSQL and similar platforms, a DoS bug may affect helper utilities or negotiation paths rather than the main data engine, but the operational impact can still be severe.