Need

Implementation of proper data validation for HTTP headers

Context

• Usage of Java for building robust and scalable applications
• Usage of javax.servlet for Java Servlet development
• Usage of javax.servlet.http for handling HTTP requests and responses in Java Servlet applications

Description

Non compliant code

        import javax.servlet.*;
import javax.servlet.http.*;

public class VulnerableServlet extends HttpServlet {

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String headerValue = request.getHeader("Custom-Header");
        // Processing the header value without any validation
        processHeaderValue(headerValue);
    }

    private void processHeaderValue(String headerValue) {
        // Some processing logic here
    }
}
        
        

In the provided code snippet, the doPost method of the VulnerableServlet class retrieves a value from the "Custom-Header" HTTP header using the getHeader method of the HttpServletRequest object. This value is then passed to the processHeaderValue method without any form of validation.

The lack of validation on the retrieved header value could potentially lead to security vulnerabilities, such as Cross-Site Scripting (XSS) attacks or compromising the integrity of stored information. This is because an attacker could inject malicious values into the HTTP headers, which would then be processed by the server-side code.

For instance, if the processHeaderValue method uses the header value in a way that's susceptible to XSS (like outputting it directly to the client-side without proper escaping), an attacker could inject a script in the header that gets executed on the client-side. Similarly, if the header value is used in a SQL query without proper sanitization, it could lead to SQL Injection attacks.

Therefore, it's crucial to always validate and sanitize any data that's received from the client-side, including HTTP header values, to prevent potential security vulnerabilities.

Steps

• Implement data validation for the header value
• Use a whitelist approach to validate the header value
• Sanitize the header value to remove any potentially malicious content
• Implement input validation for any user-supplied data used in the processing logic

Compliant code

        import javax.servlet.*;
import javax.servlet.http.*;
import java.util.regex.Pattern;

public class SecureServlet extends HttpServlet {

    private static final Pattern VALID_HEADER_REGEX = Pattern.compile("^[a-zA-Z0-9]*$"); // Whitelist approach

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String headerValue = request.getHeader("Custom-Header");
        if (isValid(headerValue)) {
            processHeaderValue(headerValue);
        } else {
            // Handle invalid header value
            System.out.println("Invalid header value");
        }
    }

    private boolean isValid(String headerValue) {
        // Validate the header value
        if (headerValue == null || !VALID_HEADER_REGEX.matcher(headerValue).matches()) {
            return false;
        }
        return true;
    }

    private void processHeaderValue(String headerValue) {
        // Some processing logic here
    }
}
        
        

The above code fixes the vulnerability by implementing data validation for the HTTP header value.

Firstly, a whitelist approach is used to validate the header value. A regular expression pattern VALID_HEADER_REGEX is defined which only allows alphanumeric characters. This pattern is used to validate the header value in the isValid method. If the header value is null or does not match the pattern, the method returns false, indicating that the header value is invalid.

In the doPost method, before processing the header value, it is validated using the isValid method. If the header value is invalid, an error message is printed and the processing is not carried out. This prevents any potentially malicious content from being processed.

This way, the code ensures that only valid and safe data is processed, thereby preventing any XSS attacks or compromises to the integrity of the stored information.

References

• 195. Lack of data validation - Headers