🛡️ Command Injection

📌 What is Command Injection?

Command Injection is a critical web security vulnerability that occurs when an application passes unsafe user input into a system shell or command interpreter. If the input isn't properly sanitized, an attacker can inject and execute arbitrary OS commands on the server.

🔍 Why Does It Happen?

Command injection typically arises when developers use functions like:

• system()
• exec()
• shell_exec() (PHP)
• Runtime.exec() (Java)
• popen()

...and directly concatenate user input without validation.

🧪 Example (PHP):

<?php
$ip = $_GET['ip'];
echo shell_exec("ping -c 1 " . $ip);
?>

If an attacker visits:

<http://example.com/ping.php?ip=127.0.0.1;ls>

The command that runs on the server is:

ping -c 1 127.0.0.1; ls

This executes ping, then lists all files in the directory (ls).