PHP Command Injection: Examples and Prevention

Command injection is a significant security risk for web applications, particularly those utilizing PHP, where attackers can execute arbitrary malicious code on a target system by exploiting vulnerabilities in how the application handles user data. This occurs when an application uses functions that make system shell calls, such as `exec`, `passthru`, and `system`, and passes unsafe or unvalidated input to these functions. Examples include using URL parameters, POST data, cookies, HTTP headers, or uploaded files to craft malicious requests that can alter the intended functionality of the application, potentially leading to severe consequences like file deletion. To prevent such vulnerabilities, developers are advised to avoid direct shell execution functions, opt for PHP's built-in alternatives like `unlink` or `rmdir`, and ensure proper validation of user inputs using functions like `filter_input`. Additionally, implementing automated tools, such as StackHawk, can help monitor code changes and detect vulnerabilities before they reach production, thereby enhancing the security posture of PHP applications.