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

Cross-site scripting is a popular and widespread attack, in which an adversary injects scripts into a web application. Web applications often use the same origination policy, which prevents scripts on the page from accessing data from different sources if their origins do not match Because Spring Boot takes security seriously and because its Security module sets security standards it is robust and flexible use so, developers like possible At least you can worry about security.

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

Java

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);
    }
}

Step-by-Step Implementation to Prevent Cross-Site Scripting (XSS) in a Spring Application

Here are the steps to prevent Cross-Site Scripting (XSS) in a Spring Application.

Step 1: Provide a securityFilterChain bean

We must set up our application to deliver a Content-Security-Policy header by giving a SecurityFilterChain bean in order to allow it:

Java

@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
}

Step 2: Add Maven Dependencies

We can include dependencies that provide extra functionality or security-related technologies to improve the security of our Spring application and help prevent Cross-Site Scripting (XSS).

<dependency>
    <groupId>org.owasp.encoder</groupId>
    <artifactId>owasp-java-encoder</artifactId>
    <version>2.5.3</version> 
</dependency>

Step 3: Make the protection filter against XSS

In order to stop XSS attacks, the XSSFilter intercepts incoming requests and performs the required sanitization.

Java

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);
       
}

• The XSSRequestWrapper class is an extension of HttpServletRequestWrapper.
• It overrides the getParameterValues function and uses the sanitizeInput method, which uses the OWASP Java Encoder to encode HTML, to sanitize each parameter value.
• By using this wrapper, you can make sure that any potentially hazardous input is cleaned up before being processed further.

Step 4: Setup of an XSSFilter

In order to avoid Cross-Site Scripting assaults, the filter applies the XSSFilter logic, which includes sanitization methods, to all incoming requests.

Java

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;
    }
}

Step 5: Update the JSON Sanitization Wrapper

In order to encapsulate the original request and override the getInputStream function to sanitize the JSON body using OWASP Java Encoder before processing it further, this defines an XSSRequestWrapper class that extends HttpServletRequestWrapper.

Java

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);
    }
}

• HttpServletRequestWrapper is extended by XSSRequestWrapper. This enables it to encapsulate an already-existing HttpServletRequest and change its functionality by overriding particular methods.
• To intercept and alter the request’s input stream, the getInputStream function is overwritten.
• An ObjectMapper instance is created. This might be used for further request processing
• The sanitized request body is contained in a ByteArrayInputStream, which is wrapped in a new ServletInputStream.

Conclusion

So, this is preventing Cross-Site Scripting (XSS) in a Spring Application. Spring Boot takes security seriously and because its Security module implements strong and adaptable security standards, developers may worry about security as little as possible.