Command Injection is a cybersecurity vulnerability that allows attackers to execute unauthorized commands on a system by inserting malicious input into fields or interfaces that interact with operating system commands. This occurs when applications do not properly validate or sanitize user input, enabling attackers to manipulate the system's behavior. Successful command injection can lead to data breaches, system compromise, or full control over the affected device. Preventing command injection involves strict input validation, sanitization, and using secure coding practices to ensure user input cannot alter system commands.