Securing Ajax Applications

The Threats

The following are some common threats against web applications, ranging from the most common and dangerous forms of cross-site scripting to more legacy vulnerabilities such as buffer overflows and other data handling issues.

Cross-Site Scripting (XSS)

Cross-site scripting (XSS) is a common form of web attack where malicious script or other code that is included in an HTTP response is involuntarily executed by the user's browser. These types of attacks can take almost any form and can be extremely dangerous. Often the attacks include sending private data such as cookies to an attacker. This can be done by redirecting the victim's browser to a web site controlled by the attacker.

Usually, identity theft is what the attackers are looking for here. Attackers steal session identifiers or a user's login credentials and impersonate that victim on legitimate sites. Web applications can be used as a mechanism to transport attacks to an end user's browser. Successful attacks can disclose session tokens, spoof content, or otherwise trick the victim into believing they are on a legitimate web site. After an attacker has navigational control of the victim's session, the game is over.

XSS comes in two basic flavors:

Reflected XSS

Data is reflected immediately back to the browser from data injected on the URL or request—the idea being an attacker formulates a link that includes the malicious script, and the victim clicks that link:

<!-- Reflected XSS example --> <%= request.getParameter("myVar"); ...