Runtime.exec is a Java API call used to start an operating-system process from code. Instead of staying inside the Java Virtual Machine, the program can invoke a shell, run a utility, or launch another executable with supplied arguments. That makes it a powerful bridge between application logic and the host operating system.
In cyber security, Runtime.exec matters because it turns code execution inside a Java application into possible host control. If an attacker can inject Java code, abuse a plugin, or exploit a server-side deserialization flaw, this call may be used to run commands, read files, create users, or download additional tools. Defenders look for it in code review, static analysis, and runtime monitoring because command-spawning behavior is often a sign of dangerous functionality. Safer designs avoid direct shell calls, validate every input that reaches process creation, and restrict the permissions of the service account so that a successful abuse chain has less impact.