Prevent Cross-Site Scripting (XSS) in a Spring Application

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
public class MyController {

    @RequestMapping("/form")
    public String showForm() {
        return "form";
    }

    @PostMapping("/submit")
    public String submitForm(@RequestParam String userInput, Model model) {
        // Validate and sanitize user input
        String sanitizedInput = validateAndSanitizeInput(userInput);

        // Pass the sanitized input to the template
        model.addAttribute("sanitizedInput", sanitizedInput);

        return "result";
    }

    private String validateAndSanitizeInput(String input) {
        // Perform input validation and sanitation based on your requirements
        // For simplicity, we'll use HTML encoding as an example
        return org.owasp.encoder.Encode.forHtml(input);
    }
}

@Configuration
public class SecurityConf {

    @Bean
    // Configuring a SecurityFilterChain bean for setting up security headers
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception 
    {
        http.headers(headers ->
                // Configure XSS protection header
                headers.xssProtection(
                        xss -> xss.headerValue(XXssProtectionHeaderWriter.HeaderValue.ENABLED_MODE_BLOCK)
                ).contentSecurityPolicy(
                        // Configure Content Security Policy to allow scripts only from 'self'
                        cps -> cps.policyDirectives("script-src 'self'")
                ));
        return http.build();
    }
    // Additional comments can go here for further clarification
}

import org.owasp.encoder.Encode;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class XSSRequestWrapper extends HttpServletRequestWrapper {

    // Constructor to initialize the wrapper with the original request
    public XSSRequestWrapper(HttpServletRequest request) {
        super(request);
    }

    // Override the method to get parameter values and sanitize each value
    @Override
    public String[] getParameterValues(String parameter) {
        // Get the original parameter values from the wrapped request
        String[] values = super.getParameterValues(parameter);

        // If the original values are null, return null
        if (values == null) {
            return null;
        }

        // Create an array to store the sanitized values
        int count = values.length;
        String[] sanitizedValues = new String[count];

        // Iterate through the original values, sanitizing each one
        for (int i = 0; i < count; i++) 
        {
            sanitizedValues[i] = sanitizeInput(values[i]);
        }

        // Return the array of sanitized values
        return sanitizedValues;
    }

    // Method to sanitize the input using OWASP Java Encoder
    private String sanitizeInput(String input) {
        return Encode.forHtml(input);
       
}

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class WebConfig {

    // Configure and register the XSSFilter as a bean
    @Bean
    public FilterRegistrationBean<XSSFilter> filterRegistrationBean() {
        // Create a new FilterRegistrationBean for XSSFilter
        FilterRegistrationBean<XSSFilter> registrationBean = new FilterRegistrationBean<>();

        // Set the XSSFilter instance as the filter to be registered
        registrationBean.setFilter(new XSSFilter());

        // Specify the URL patterns to which the filter should be applied
        registrationBean.addUrlPatterns("/*");

        // Return the configured FilterRegistrationBean
        return registrationBean;
    }
}

import com.fasterxml.jackson.databind.ObjectMapper;
import org.owasp.encoder.Encode;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.ByteArrayInputStream;
import java.io.IOException;

public class XSSRequestWrapper extends HttpServletRequestWrapper {

    private final ObjectMapper objectMapper = new ObjectMapper();

    // ... (other methods)

    @Override
    public ServletInputStream getInputStream() throws IOException {
        // Get the original input stream from the wrapped request
        ServletInputStream originalInputStream = super.getInputStream();

        // Read the entire request body into a String
        String requestBody = new String(originalInputStream.readAllBytes());

        // Sanitize the JSON body using the sanitizeInput method
        String sanitizedBody = sanitizeInput(requestBody);

        // Create a new ServletInputStream with the sanitized body
        return new ServletInputStream() {
            private final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(
                    sanitizedBody.getBytes()
            );

            @Override
            public int read() throws IOException {
                return byteArrayInputStream.read();
            }

            @Override
            public boolean isFinished() {
                return byteArrayInputStream.available() == 0;
            }

            @Override
            public boolean isReady() {
                return true;
            }

            @Override
            public void setReadListener(ReadListener readListener) {
                // No implementation needed for this example
            }
        };
    }

    // Method to sanitize the input using OWASP Java Encoder
    private String sanitizeInput(String input) {
        return Encode.forHtml(input);
    }
}