An application server is software that runs web applications and provides the services they need, such as authentication, session handling, database access, and integration with other systems. In enterprise environments, one application server can host multiple business apps, making it a shared control point for users and back-end services.
In cyber security, that central role makes application servers high-value targets. If attackers find a weakness in the server layer, they may bypass login checks, steal sessions, or execute code on the host and pivot into hosted applications. Defenders treat application servers as critical infrastructure: they inventory exposed instances, patch them quickly, restrict network access, and monitor for unusual authentication failures, server errors, or unexpected process activity. Because so many services depend on the same platform, a single flaw can affect many applications at once.