What is Command Injection?

Command Injection is a vulnerability that occurs when an application passes unsafe user-supplied input directly to the operating system's shell or command interpreter. This allows an attacker to execute arbitrary commands on the underlying OS. Essentially, the attacker takes advantage of improper handling of inputs in the application's code to inject malicious commands.

Impact of Command Injection:

1. Remote Code Execution (RCE): Attackers can gain complete control over the system, potentially leading to full compromise.
2. Data Exfiltration: Attackers can extract sensitive information from the target system, such as configuration files, environment variables, or database contents.

How to Prevent Command Injection:

1. Input Validation:
   • Ensure strict validation of user inputs, allowing only predefined formats (e.g., whitelist acceptable inputs) and rejecting potentially dangerous characters like &, |, ;, or &&.
2. Avoid Using Functions That Directly Interact with the OS:
   • For example, in PHP, avoid using functions like system(), exec(), shell_exec(), or passthru(). Instead, use safer alternatives such as language-native functions for handling file operations or database queries.
3. Use Parameterized APIs or Functions:
   • Utilize APIs or functions that don't directly interact with the OS or that handle commands securely. For example, in Java, Runtime.exec() can be dangerous, but using library functions that don't invoke the OS shell can reduce the risk.
4. Escape Input Properly:
   • If interacting with the shell is unavoidable, ensure that all inputs are escaped to prevent injection attacks. Tools like escapeshellcmd() in PHP help reduce the risk.
5. Least Privilege Principle:
   • Run the application with the minimum necessary privileges to limit the damage if an injection occurs.

Command Injection checklists

1. Check Input Points

• identify input fileds ,forms , URL parameters , headers where user input is passed to system commands
• check file upload mechanisms where filename or file content might be executed by the server