To answer this question, let's go through each option to understand why it is correct or incorrect:
Option A) Firewall - Firewalls help protect against unauthorized access to your network by monitoring and controlling incoming and outgoing network traffic. While firewalls can help prevent certain types of vulnerabilities, they are not the most effective preventive measure against all vulnerabilities. Therefore, this option is incorrect.
Option B) Input Validation - Input validation is the process of checking and validating user input to ensure that it meets specified criteria. By implementing input validation, you can prevent common vulnerabilities such as SQL injection, cross-site scripting (XSS), and command injection. This option is correct because input validation is an effective preventive measure against various vulnerabilities.
Option C) Updated Antivirus - While having an updated antivirus program is essential for protecting against malware and viruses, it is not the most effective preventive measure against all vulnerabilities. Antivirus software primarily focuses on detecting and removing malicious software, but it may not prevent vulnerabilities caused by insecure coding practices or configuration errors. Therefore, this option is incorrect.
Option D) Extension check for file - Checking the extension of a file can help prevent certain types of vulnerabilities, such as file upload vulnerabilities. By validating the file extension, you can ensure that only allowed file types are uploaded, reducing the risk of executing malicious code. However, this measure alone is not sufficient to prevent all vulnerabilities. Therefore, this option is incorrect.
The correct answer is Option B) Input Validation. This option is correct because input validation is a fundamental preventive measure that helps protect against various vulnerabilities.