Command Injection

What is Command Injection?

  • Command Injection is a type of security vulnerability where an attacker can execute arbitrary commands on a host operating system via a vulnerable application.

  • It typically occurs in web applications that improperly process user input to execute system-level commands.

How Does Command Injection Occur?

  • Vulnerable Input Processing: When user input is not properly validated or sanitized, and directly used in a system command.

  • Commonly Affected Languages/Technologies: PHP, Java, Python, Shell scripts, SQL databases with system command functions.

Examples of Command Injection

  • A web form that takes a user input (like a username) and uses it in a system command without proper validation.

  • URL parameters or HTTP headers that are concatenated directly into system commands.

Basic Example

  • Unsafe code in PHP: shell_exec('ping ' . $_GET['ip']);

  • In this example, if an attacker inputs 8.8.8.8; rm -rf /, it could lead to the execution of a harmful command (rm -rf /).

Impact

  • Data Breach: Unauthorized access to or theft of data.

  • System Compromise: Gain control over the host system.

  • Denial of Service: Disrupt services by executing resource-intensive commands.

Prevention and Mitigation

  • Input Validation: Strictly validate user inputs for expected formats.

  • Use Safe APIs: Use language-specific safe APIs that abstract command execution.

  • Escaping Inputs: Properly escape special characters in user inputs.

  • Least Privilege Principle: Run applications with the least privileges necessary.

  • Regular Security Auditing: Regularly audit code and applications for vulnerabilities.

Testing for Command Injection

  • Manual Testing: Attempt to input system commands through the application.

  • Automated Tools: Use security scanning tools like OWASP ZAP, Burp Suite.

  • Code Review: Regularly review code for potential vulnerabilities.

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