OS (Operating System) injection, also known as Command Injection, is a web security vulnerability that allows an attacker to execute arbitrary operating system commands on a server or host running a web application. It occurs when user-supplied input is not properly validated or sanitized before being passed to system commands or shell interpreters.
Web applications sometimes need to interact with the underlying operating system to perform certain tasks such as executing shell commands, running system utilities, or accessing file systems. If the application does not handle user input correctly, an attacker can manipulate the input to inject malicious commands that are executed by the operating system.
Here's an example to illustrate how OS injection works:
Suppose there is a web application that allows users to submit feedback and the application uses a command to save the feedback to a file on the server:
```
$feedback = $_POST['feedback'];
$command = "echo '$feedback' >> feedback.txt";
exec($command);
```
In this example, the application directly concatenates the user-supplied feedback into a shell command without proper validation or sanitization. An attacker could take advantage of this by submitting the following feedback:
```
This is my feedback'; rm -rf /; #
```
The injected command `rm -rf /` is a dangerous command that deletes all files and directories on the server. The `;` character is used to terminate the original command, and the `#` symbol is used to comment out any remaining code.
As a result, the executed command becomes:
```
echo 'This is my feedback'; rm -rf /; #' >> feedback.txt
```
This leads to the deletion of the entire file system on the server, causing significant damage.
To prevent OS injection attacks, it is crucial to validate and sanitize all user input and avoid executing system commands directly with user-supplied data. Instead, application developers should use safe API functions or libraries that handle user input securely, such as parameterized commands or API calls specific to the programming language or framework being used.
Regular security testing, input validation, and following secure coding practices are essential in mitigating OS injection vulnerabilities and ensuring the security of web applications.
