Command injection vulnerability is a security flaw that occurs when an application accepts and executes external inputs from users without properly validating or sanitizing them. This vulnerability typically affects web applications that interact with external systems or execute shell commands on the server.

In a command injection attack, an attacker exploits this vulnerability by injecting malicious commands into the application’s input fields or parameters. These commands can be executed within the context of the application’s environment, potentially allowing the attacker to perform unauthorized actions, such as executing system commands, accessing sensitive information, or compromising the integrity of the system.

For example, consider a web application that allows users to search for files on the server by entering a filename. If the application does not properly validate user input and directly passes it to a system command without proper sanitization, an attacker could input a malicious command along with the filename, such as appending ; rm -rf /, which could lead to the deletion of important files or directories on the server.

To prevent command injection vulnerabilities, developers should implement strict input validation, use parameterized queries or prepared statements for database queries, and avoid executing external commands with user-supplied input. Additionally, employing proper access controls and limiting the privileges of the application can help mitigate the impact of potential attacks.