Testing for AJAX: introduction

4.11 AJAX Testing
AJAX, an acronym for Asynchronous JavaScript and XML, is a web development technique used to create more responsive web applications. It uses a combination of technologies in order to provide an experience that is more like using a desktop application. This is accomplished by using the XMLHttpRequest object and JavaScript to make asynchronous requests to the web server, parsing the responses and then updating the page DOM HTML and CSS.

Utilizing AJAX techniques can have tremendous usability benefits for web applications. From a security standpoint, however, AJAX applications have a greater attack surface than normal web applications, and they are often developed with a focus on what can be done rather than what should be done. Also, AJAX applications are more complicated because processing is done on both the client side and the server side. The use of frameworks to hide this complexity can help to reduce development headaches, but can also result in situations where developers do not fully understand where the code they are writing will execute. This can lead to situations where it is difficult to properly assess the risk associated with particular applications or features.

AJAX applications are vulnerable to the full range of traditional web application vulnerabilities. Insecure coding practices can lead to SQL injection vulnerabilities, misplaced trust in user-supplied input can lead to parameter tampering vulnerabilities, and a failure to require proper authentication and authorization can lead to problems with confidentiality and integrity. In addition, AJAX applications can be vulnerable to new classes of attack such as Cross Site Request Forgery (XSRF).

Testing AJAX applications can be challenging because developers are given a tremendous amount of freedom in how they communicate between the client and the server. In traditional web applications, standard HTML forms submitted via GET or POST requests have an easy-to-understand format, and it is therefore easy to modify or create new well-formed requests. AJAX applications often use different encoding or serialization schemes to submit POST data making it difficult for testing tools to reliably create automated test requests. The use of web proxy tools is extremely valuable for observing behind-the-scenes asynchronous traffic and for ultimately modifying this traffic to properly test the AJAX-enabled application.

In this section we describe the following:

4.11.1 AJAX Vulnerabilities 4.11.2 How to test AJAX