What is the primary mitigation technique for Cross-Site Scripting vulnerabilities?

The primary mitigation technique for Cross-Site Scripting (XSS) vulnerabilities is validating and sanitizing input data. XSS attacks occur when an attacker is able to inject malicious scripts into web applications, typically via user input fields. By validating input, developers can ensure that only expected data formats are accepted, thus reducing the risk of script injection. Sanitizing involves cleaning the input by stripping out or encoding characters that could be interpreted as executable code, further protecting the application from XSS.

Implementing firewalls and proxies can help monitor and control data traffic but does not directly address how the web application handles input data. Encrypting data is important for protecting sensitive information during transmission, but it does not mitigate the risk of XSS by itself. Disabling user input fields would prevent legitimate user interactions and limit the functionality of web applications, which is not practical and does not address the root cause of XSS vulnerabilities. Therefore, validating and sanitizing input data is the most effective way to protect against XSS vulnerabilities, ensuring that data processed by the application is safe and does not contain harmful scripts.