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Lack of data validation - Header x-amzn-RequestId

Need​

Implementation of strict data validation for the x-amzn-RequestId Header

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance
  • Usage of javax.servlet-api for building Java web applications with Servlets

Description​

Non compliant code​

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public void doSomething(HttpServletRequest request, HttpServletResponse response) {
    String requestId = request.getHeader("x-amzn-RequestId");
    // Use the requestId directly without validation
    // ... 
}

In the above code snippet, the application retrieves the x-amzn-RequestId header from the HTTP request and uses it directly without any form of validation.

This is a potential security vulnerability as it allows an attacker to inject potentially dangerous character strings. Since the application does not control server side permission to modify certain fields, an attacker can manipulate the x-amzn-RequestId header to perform malicious activities.

For instance, if the x-amzn-RequestId is used in a database query, an attacker could inject SQL commands leading to an SQL Injection attack. Similarly, if it is used in an HTML response, it could lead to Cross-site Scripting (XSS) attacks.

Therefore, it is crucial to validate data received from HTTP headers to ensure that they conform to the expected format and do not contain any dangerous characters.

Steps​

  • Implement data validation for the x-amzn-RequestId header
  • Validate the format and content of the requestId
  • Reject or sanitize any potentially dangerous character strings
  • Use a whitelist or regular expressions to define the allowed characters or format
  • Consider using a library or framework that provides built-in validation mechanisms
  • Implement server-side permission checks to control modifications to certain fields

Compliant code​

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.regex.Pattern;

public void doSomething(HttpServletRequest request, HttpServletResponse response) {
    String requestId = request.getHeader("x-amzn-RequestId");
    
    // Define a whitelist of allowed characters in the requestId
    String whitelist = "^[a-zA-Z0-9-]*$";
    
    // Use a regular expression to validate the requestId
    Pattern pattern = Pattern.compile(whitelist);
    
    if (pattern.matcher(requestId).matches()) {
        // If the requestId is valid, proceed with the rest of the code
        // ...
    } else {
        // If the requestId is not valid, reject the request or sanitize the requestId
        // ...
    }
}

The updated code includes data validation for the x-amzn-RequestId header. This is done by defining a whitelist of allowed characters (in this case, alphanumeric characters and hyphens) and using a regular expression to check if the requestId matches this pattern.

If the requestId is valid (i.e., it only contains characters from the whitelist), the code proceeds as normal. If the requestId is not valid (i.e., it contains characters not in the whitelist), the code rejects the request or sanitizes the requestId. This could involve removing the invalid characters or replacing them with a default value.

This approach helps to prevent potentially dangerous character strings from being entered in the x-amzn-RequestId header. It also provides a server-side permission check to control modifications to the requestId field.

For more robust validation, consider using a library or framework that provides built-in validation mechanisms. This can help to ensure that the validation is thorough and consistent across your application.

References​

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